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Environmental assessment, management and utilization of red mud in China
Accepted Manuscript Environmental Assessment, Management and Utilization of Red Mud in China Wanchao Liu, Xiangqing Chen, Wangxing Li, Yanfen Yu, Kun Yan PII:
S0959-6526(14)00668-4
DOI:
10.1016/j.jclepro.2014.06.080
Reference:
JCLP 4475
To appear in:
Journal of Cleaner Production
Received Date: 19 October 2013 Revised Date:
18 May 2014
Accepted Date: 27 June 2014
Please cite this article as: Liu W, Chen X, Li W, Yu Y, Yan K, Environmental Assessment, Management and Utilization of Red Mud in China, Journal of Cleaner Production (2014), doi: 10.1016/ j.jclepro.2014.06.080. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Map of red mud producers location in China
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Environmental Assessment, Management and Utilization of Red
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Mud in China
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Wanchao Liu* , Xiangqing Chen, Wangxing Li, Yanfen Yu, Kun Yan
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Zhengzhou Research Institute of CHALCO, Zhengzhou, Henan, 450041, P.R. China
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*Corresponding author: Dr. Wanchao Liu
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Email: [email protected]; Tel/Fax: +86-371-68918623.
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Abstract
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In global alumina production, red mud presents a common problem due to its alkalinity
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which can contaminate the environment. China is the largest producer both of alumina
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and red mud in the world. A nationwide investigation was carried out to evaluate the
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status of residue generation, disposal of and utilization of red mud. Analysis of this
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study revealed that the characteristics of red mud depend on ore sources and refining
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processes. Red mud should be categorized as general industrial waste rather than
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hazardous waste. In China, red mud is considered to be a useful resource rather than a
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contamination. By using contemporary technology, it is possible to utilize 20% of high-iron Bayer red mud and 20% of sintering red mud. More research should be focused on utilization of low-iron Bayer red mud. Keywords
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Red mud, Disposal, Utilization, Investigation, Waste management
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Red mud (Bauxite residue) is a solid waste generated in alumina refining from bauxite.
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It cannot be disposed easily due to its alkali content which can contaminate the
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environment. Mostly, it is pumped into holding ponds. Red mud presents a problem as
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it takes up land and can neither be built on nor farmed, even when it has been dry
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(Rudraswamy and Prakash, 2014). Due to this situation, research has been done to find
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a suitable way to utilize the mud for other applications.
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China is the largest producer of both alumina and red mud in the word. In order to get
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data on the residue generation, disposal and utilization of red mud, a nationwide
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investigation was carried out by the National Engineering Research Centre for
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Aluminum Metallurgy and Zhengzhou Research Institute of CHALCO (Aluminum
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Corporation of China Limited) with the support of the Ministry of Environmental
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Protection. Part of the investigation results are presented in this paper to offer a
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reference for international peers in management of red mud.
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1. Alumina Production & Red Mud There are three processes commercially applied for alumina refining, i.e. the sintering process, the Bayer process and the combination process (Bayer-sinter). The sintering
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process was the sole process applied in China before the 1990s because of its high
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alumina refining ratio from the diaspore bauxite. However, the energy consumption of
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the sintering processes is much higher than that of two other processes. In 1993, the
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Bayer process was used in Shandong with imported gibbsite bauxite. The high
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temperature Bayer process and the flotation Bayer process were also successfully
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applied with China diaspore bauxite. Presently, the sintering process is mainly used to
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produce chemical alumina. The sintering process is considered as an important method
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to refine alumina from low grade bauxite, fly ash and other resources, however, few of
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these alternatives is applied commercially in China. The alumina product from the
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sintering process accounts for about 2.5% of total alumina output in 2011.
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About 3/4 of China alumina capacity is distributed in Henan, Shanxi, Guizhou, Guangxi,
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Yunnan and Chongqing, because of abundant diaspore deposits in these areas. And the
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rest 1/4 of China alumina capacity is located in Shandong Province because of its
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region advantage in ocean transport for gibbsite importing. The distribution of alumina
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refineries in China, i.e. red mud producers are shown in Fig.1. Most of the annual alumina production capacities of refineries are over 1 million tonnes per annum.
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2. Characteristics of Red Mud
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2.1 Samples and experimental methods
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Five kinds of red mud samples were collected for the study from different bauxite and
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different refining processes (Table 1). These red mud samples are representative in
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refineries in China and the world. Sample 1, 2, 3 and 4 were generated from Chinese
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diaspore. Sample 1 and samples 2 were from high temperature digestion Bayer process.
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And sample 2 has higher iron content than that of sample 1. Sample 3 and sample 4
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were collected from the combined and the sintering process, respectively. And sample
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5 was sampled from lower digestion Bayer process and it was generated from gibbsite
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bauxite imported from Indonesia.
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For X-ray fluorescence (XRF) analysis of the samples, a sub-sample was melted with
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1222 flux to produce a flat 40 mm glass tablet for analysis. The tablet was analyzed
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with a Philips PW 2404 XRF spectrometer.
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The X-Ray diffraction (XRD) analyses were made on powdered samples in a PANalytical
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multipurpose diffractometer using Co Kα radiation. Phases were identified using XPLOT for Windows and the ICDD database. The specific surface area, pore volume and pore size of samples were tested by the
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automated physisorption and chemisorption analyzer (Autosorb-1-C, Quantachrome
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Instruments). The fractal dimensions of particles were calculated from the
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adsorption-desorption data with the Frenkel-Halsey-Hill (FHH) model.
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The corrosivity and toxicity of red mud samples were tested as required by the
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standards for hazardous properties for hazardous wastes, i.e., Identification standard
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for hazardous wastes -Identification for corrosivity (Chinese national standard
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GB5085.1-2007) and Identification standard for hazardous wastes - Identification for
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extraction toxicity (Chinese national standard GB5085.3-2007), respectively.
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2.2 Compositions of red mud
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The characteristics of red mud depend on ore sources and refining processes. The
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chemical composition of the five red mud samples can be found in Table 2. Red mud
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produced from the sintering process and combined process has similar composition
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characteristics (Sample 3 and sample 4). The contents of CaO and SiO2 in the residues
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from these two processes are much higher than that from the Bayer process. The Fe2O3
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in red mud of Chinese ore (sample 1), except from Guangxi (sample 2) are much lower than that from imported ore (sample 5). The dominating mineral phases in these samples were also studied. The main composition of the red mud from the sintering process is larnite (β-2CaO·SiO2), with a
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mass ratio of over 50%. Dominating mineral compositions in Bayer process red mud are
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desilicification products (DSP), and remaining minerals of bauxite such as hematite,
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quartz etc.. There are different DSP phases in red mud from different ore and digestion
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processes (Fig. 2). When diaspore bauxite is digested in high temperature, quartz is
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reactive. Thus, there is less quartz left in sample 1 and 2, which was generated from
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diaspore, than that in sample 5, which was generated from gibbsite. To decrease the
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aluminum loss in DSP caused by more reactive silicon, lime is added into the diaspore
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slurry. So in sample 1 and 2, most of DSP phases are cancrinite and hydrogarnet, as well
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as natrodavyne.
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From view of composition, red mud in China could be classified into 4 kinds, i.e.,
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sintering process red mud, lower iron diaspore red mud from Bayer process, high iron
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diaspore red mud from Bayer process, gibbsite red mud. The proportions of 4 kinds of
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red mud in China in 2011 are shown in Fig.3. The products of red mud are calculated
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from alumina product and red mud generation ratios in related processes. As shown in
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Fig.3, 7% of red mud is generated from sintering process, 26% of red mud is generated from imported gibbsite, and 67% of red mud is generated from the Bayer process with local diaspore including 49% from low iron bauxite and 18% from high bauxite.
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2. 3 Particle Properties
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Red mud is an aggregate of particles with different fineness. Research shows that the
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specific surface areas and pore characteristics of red mud are also different because of
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bauxite ore and refining processes (Table 2). The specific surface area of red mud
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becomes larger with higher pore volume and smaller with average pore size.
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Particularly, the specific surface area of red mud from gibbsite is much larger than
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other samples, the reason for this may be the easy digestion properties of gibbsite
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from bauxite, which forms tiny channels in red mud particles. The difference between
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sample 1 and sample 2 is possibly caused by the relatively hard hematite particles in
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sample 2. In the sintered red mud, an amount of molten phase is generated which
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leads to higher density and smaller specific surface area. The fractal dimensions of
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particles
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Frenkel-Halsey-Hill (FHH) model. The data quantifies the structural characteristics of
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the red mud particles. From the data, fractal dimension (D) of samples are varying
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between 2.75 - 2.82, which show that red mud particles are fractal. Sample 4 is revealed to be coarser than others. 2.4 Environmental Properties "Hazardous waste" is a category designated by the Basel Convention on the Control of
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Trans boundary Movements of Hazardous Wastes and Their Disposal for substances
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which possess one or more hazardous properties, i.e. corrosivity, toxicity, ignitability,
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reactivity and/or infectivity. From common sense reasoning, the ignitability of red mud
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is poor, and the reactivity and infectivity of red mud are weaker than that of hazardous
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materials. The corrosivity and toxicity test results from the red mud samples show that
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(Table 3) the pH values of samples are lower than corrosivity limit (12.5) and the toxic
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element contents of samples are lower than toxicity limits. Thus these red mud
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samples are general industrial waste but not hazardous waste. Red mud is not
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categorized as a hazardous material in the Chinese National Catalogue of Hazardous
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Wastes (2008), which is issued by the Chinese government to reinforce the
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management of hazardous waste.
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After the Ajka tragedy in Hungary, public attention was focused on the environmental
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properties of red mud. The Hungarian government stated that the mud is not
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poisonous (Government of Hungary, 2010), and the Hungarian Academy of Sciences
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stated that the heavy metal concentrations were not considered dangerous for the environment. This opinion was also supported by Enserink (2010). What should be mentioned here is that, the pH of red mud supernatant liquor usually is 12-14, which is hazardous to the surrounding ecology. It is believed that the main
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damages in the Ajka accident caused first by arose from the high pH of the mud slurry,
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which was responsible for both severe chemical burns to humans and animals and
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killing specimens in the rivers and contaminated soils. In order to safely dispose of red
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mud, it is crucial to wash, dewater, and neutralize before it is discharged.
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3. Disposal of red mud in China
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Investigation of disposal data was obtained from 11 alumina plants (in operation or in
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construction). The total alumina capacity of these 11 plants is 12.858 million tonnes
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per year (Table 4), which is about 30% of national alumina capacity. The data gathered
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from the 11 plants was used to estimate the generation ratios of red mud from
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different processes. It can be predicted that, until the end of 2011, there are 250
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million tonnes of red mud in over 60 storage sites on 25 km2 land in China.
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Until the end of 2011, in these 11 refineries, there are 14 available red mud storages, 5
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closed storages and 10 storages in planning or construction stage. From the obtained
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data, wet disposal technology is applied the most widely. In the 19 old storages, which
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are in using or closed, only 3 storages applied dry or semi-dry processes. Due to the environmental and safety factors it is a trend to apply dry and semi-dry processes in new sites. In the 10 sites which are in construction or in planning, 3 of them will use
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dry process, and 2 will use the semi-dry process; the other 5 sites will apply the wet
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disposal technology because of local ravine terrain.
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Most of the disposal sites of the 11 alumina plant are being operated normally as
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required by a series of laws and regulations issued on management of red mud and
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general waste. However, few closed red mud storages were ecologically restored as
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required. The reclamation of the storages should be stressed in the future to decrease
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the environmental impact of red mud.
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Red mud is characterized as alkalinity, high moisture content and poor cementing
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properties, that is different from other industrial wastes. For normalization of red mud
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disposal storage designing, the Design Code of Red Mud Storage Pond with Dry Process
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is being drafted by specialist agencies. All of the procedures concerned in the dry
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disposal of red mud will be normalized in the code from site selection, designing,
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damming, seepage-proofing, flood drainage, water backing, residue transporting,
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operation management, to safety monitoring.
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4. Utilization of Red Mud The utilization of red mud as a second resource can be useful to reduce management cost. It is one of the objectives of the government of China to utilize 20% of fresh red
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mud by the end of 2015 (MIIT and MOST, 2010). Substantial research and field
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applications have been carried out in this field (Wanchao et al., 2009a). The status of
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red mud utilization technologies are shown in Table 5.
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The red mud from the sintering or combined process is pozzolanic, so it is useful in
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producing building and construction material. Around 10 million tonnes of red mud
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were used in Portland cement production commercially. However, it was terminated
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due to the new cement standard which increased the limitation of Na2O+K2O content
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because of alkali-aggregate reaction (Tongsheng et al, 2013). The Shandong Branch of
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CHALCO built a pilot plant for non-sintering brick production using the red mud from
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sintering process (Jiakuan and Bo, 2008). The quality of bricks was found to satisfy the
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local building material requirements, but the efflorescence is the biggest hurdle to high
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quantity addition of red mud in building materials. A demonstrated road 4 km long was
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built with red mud road base material. The application of red mud in road building
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depends on the distance between the refinery and the road construction sites, because
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the consumer does not want to pay high transporting cost. Every year, 150-200 kt sintering red mud is used in building material production and construction. Over 50 ktpa of red mud from sintering and combination process was used to build the red mud dams and the qualities of dams are satisfying.
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A plant has been in operation to produce glass-ceramics with red mud in Shanxi from
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2013. About 10 kt red mud will be consumed annually in 450,000 m2 glass-ceramics
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production. The red mud which is used in the plant is produced by sintering process
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from local diaspore bauxite.
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For the residue from the Bayer process which has high iron content, iron concentrating
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is carried out. The process is applied in several plants which are fed with local high iron
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bauxite and imported bauxite from Indonesia, Australia and Fiji. The physical process
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works well in iron recovery from red mud. The bauxite residue was separated into
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three parts, i.e., the iron ore, sand and fine mud and was accomplished through
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cyclone separator, magnetic separator, spiral chute and shaking table sequentially. The
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total Fe2O3 content in the concentrate varies from 50-70%. The sand was used as a raw
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material in concrete bricks. The economic assessment showed that the process is
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viable. From 2010, around 10 million tonnes of the residue were treated and at least
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80-100 kt of iron ore was concentrated annually. The concentrate is used in iron and
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steel production and cement production. The high temperature reduction of hematite to magnetite or metallic iron was also carried out in lab to improve the concentrate levels and the recovery rate (Wanchao et al., 2009b, 2012). Based on the fine particle size, a filler can be produced from raw red mud and the
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tailings of iron ore separation from red mud. The filler can be used in polymer products.
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The technology is applicable to all kinds of red mud. Unfortunately, the market
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requirement for the filler is too small compared with the production of red mud.
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In order to use the lower iron red mud, recovery of rare earth elements (Dongyan &
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Chuansheng, 2012), and adsorption of heavy metal from contaminated water (Yi et al,
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2010) and acid from gas (Hongtao et al, 2013) are also being researched. However,
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these processes are not yet commercially applicable until now because of economic or
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engineering reasons. For example, HCl is applied in rare elements extraction from red
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mud in present technologies. So equipment cost on the extraction is high because most
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of equipment should be preservative treated. When red mud is used for heavy metals
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adsorption, more residues will be generated than common adsorbents. The
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desulfurization system cannot run for long term stably due to serious scaling caused by
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red mud desulfurizer.
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From our present technological status, it is possible to utilize 20% of high-iron Bayer
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red mud and 20% of sintering red mud. But in China, there is 49% of red mud from Bayer process with lower iron diaspore. Red mud utilization is still a challenge for China.
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5. Conclusions
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The characteristics of red mud depend on ore sources and refining processes. Generally,
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red mud should be categorized as general industrial waste rather than hazardous waste.
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The dry disposal process and the semi-dry disposal process should be encouraged or
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even be driven by legislative compliance to be applied in more plants. The dewatering,
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soda recovery, neutralization and ecological restoration should be emphasized due to
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environmental safety. Great progresses are being obtained in China on red mud
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treatment. By using contemporary technology, it is possible to utilize 20% of high-iron
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Bayer red mud and 20% of sintering red mud. However, more research should be
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focused on utilization of low-iron Bayer red mud.
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As well as China, the treatment of red mud is still a challenge to global alumina industry.
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Open atmospheres about the treatment and utilization of red mud should be built both
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in China and in the international community.
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Acknowledgement
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Authors would like to acknowledge the funding of the China Ministry of Environmental Protection (No. 1441100023) and National Natural Science Foundation of China (Grant No. 51304216).
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244 Reference
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Dongyan L., Chuansheng W. (2012). Stockpiling and Comprehensive Utilization of Red Mud Research
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Progress. Materials, 5, 1232-246.
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Enserink M. (2010). After red mud flood, scientists try to halt wave of fear and rumors. Sci., 330:
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432–433.
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Government
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http://redsludge.bm.hu/?p=59#more-59.
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Hongtao L., Kuihua H., Shengli N., Chunmei L., Mengqi L., Hui L. (2013). Experimental study and
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mechanism analysis of modified limestone by red mud for improving desulfurization. Cleaner
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Combustion and Sustainable World. DOI:10.1007/978-3-642-30445-3_65.
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Jiakuan Y., Bo X. (2008). Development of unsintered construction materials from red mud wastes
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produced in the sintering alumina process. Const. Buil. Mat., 22: 2299 - 307.
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Ministry of Industry and Information Technology (MIIT), and Ministry of Science and Technology
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(MOST),
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http://www.miit.gov.cn/n11293472/n11293832/n12843926/n13917027/14011841.html
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Rudraswamy M.P., Prakash K. B. (2014). An experimental investigation on the effect of alternation of
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Red
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Guidance
on
sludge
and
detoxification.
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(2010).
Comprehensive
Utilization
of
Red
Mud.
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(2010).
Hungary
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of
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alternate wetting and dry on the properties of concrete produced by red mud. Int. J. Advanced
Research, 2(1): 473-484.
Yi L., Yetang H., Duojun W., Yongxuan Z. (2010). Effect of red mud on the mobility of heavy metals in
mining-contaminated soils. Chinese J. Geochemistry, 29(2): 191-196.
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Tongsheng Z., Peng G, Pinhai G., Jiangxiong W., Qijun Y. (2013). Effectiveness of novel and traditional
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methods to incorporate industrial wastes in cementitious materials—An overview. Res. Cons.
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Recycl., 74: 134-143
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Wanchao L., Jiakuan Y., Xiao B. (2009a). Review on treatment and utilization of bauxite residues in
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China. Int. J. Mineral Proc., 93, 220-231.
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Wanchao L., Jiakuan Y., Bo X. (2009b). Application of Bayer red mud for iron recovery and building
271
material production from alumosilicate residues. J. Hazard. Mat., 161: 474 - 478.
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Wanchao L., Shouyi S., Ling Z., Sharif J., Jiakuan Y. (2012). Experimental and simulative study on
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phase transformation in Bayer red mud soda-lime roasting system and recovery of Al, Na and Fe.
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Min. Eng., 39: 213-218.
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Fig.1 Map of red mud producers location in China
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1, Natrodavyne; 2, Cancrinite; 3, Calcite; 4, gibbsite;
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5, Diaspore; 6, Hematite; 7, Al(OH)3; 8, Alumogoethite; 9, Quartz; 10, Hydrogarnet.
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Fig.2 XRD patterns of Bayer red mud samples
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287 High iron diaspore red mud from Bayer process, 18%
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Red mud from sintering and combined process, 7%
High iron gibbsite red mud from Bayer process, 26%
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Fig.3 Proportion of 4 kinds of red mud in China (2011)
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Low iron diaspore red mud from Bayer process, 49%
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Sample No.
1
Fed bauxites
diaspore
Bauxite origin
Henan, China
Processes
Bayer
Bayer
Digestion temperature
260oC
260oC
3
4
5
diaspore
gibbsite
Shandong, China
Indonesia
Combined
Sintering
Bayer
N/A
N/A
140 oC
diaspore Shanxi, China
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diaspore (high iron) Guangxi, China
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Table 1 Red mud samples from different refiners
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1
2
3
4
5
Al2O3, %
25.48
18.87
10.5
8.32
17.85
SiO2, %
20.58
8.87
22.2
32.5
20.48
Fe2O3, %
11.77
34.25
6.75
5.7
32.14
TiO2, %
4.14
6.05
2.55
/
3.57
K2O, %
2.07
0.08
0.85
/
/
Na2O, %
6.55
4.35
3.00
2.33
6.75
CaO, %
13.97
13.59
42.25
41.62
8.21
MgO, %
1.54
0.41
2.46
/
/
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Samples
11.65
7.37
5.31
/
30.72
Pore volume, ×10-3cm3/g
11.15
7.05
4.75
/
22.94
Average pore size, nm
3.83
3.82
3.58
/
2.99
Fractal dimension
2.75
2.75
2.78
/
2.82
EP
Specific surface area,m2/g
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Table 2 Chemical & physical characteristics of red mud from different refiners
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Note: “/” means the datum was not tested.
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Table 3 Testing results for corrosivity and extraction toxicity of bauxite residue
Unit pH (corrosivity)
1
2
3
11.33
10.66
12.18
5
Limits*
9.77
<12.5
<0.05
5
1.14
100
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mg/L
0.23
0.21
<0.05
F-
mg/L
2.03
2.03
0.18
CN-
mg/L
0.91
0.91
0.26
0.2
5
Total Ag
mg/L
<0.01
<0.01
<0.01
<0.01
5
As
mg/L
<0.1
<0.1
<0.1
<0.1
5
Ba
mg/L
<0.003
<0.003
<0.003
<0.003
100
Be
mg/L
<0.0003
<0.0003
<0.0003
<0.0003
0.02
Cd
mg/L
<0.003
<0.003
<0.003
<0.003
1
Cr
mg/L
0.16
0.12
<0.01
<0.01
15
Cu
mg/L
<0.01
<0.01
0.027
0.015
100
Ni
mg/L
Pb
mg/L
Se
mg/L
Zn
mg/L
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<0.01
<0.01
<0.01
5
<0.05
<0.05
<0.05
<0.05
5
<0.5
<0.5
<0.5
<0.5
1
<0.006
<0.006
<0.006
<0.006
100
<0.0005
<0.0005
<0.0005
0.1
EP
<0.01
mg/L
<0.0005
297
*: The limits of hazardous properties are reference to Identification standard for hazardous wastes
298
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Total Hg
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Cr6+
(GB5085.1-7, 2007).
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Table 4 alumina and red mud disposal data from 11 alumina plants
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Total amount of red
Processes
Alumina
Red mud
used in the
production in
production in
refinery
2010, kt
2010, kt
mud produced up
Refineries No. location
until the end of 2010,
Guizhou 1
2
Shanxi 1
Bayer
74
Bayer
860
Combined
1,860
3,080
18,690
80
280
11,000
750
850
20,650
950
934
3,500
Bayer
810
1,215
3,210
Bayer
20,00
2,600
7,500
Bayer*
0
0
0
Bayer
173
97
300
Sintering*
0
0
0
Bayer
2,050
1,460
9,520
Sintering Henan 2
Shanxi 2
7
Chongqing 1
8
Chongqing 2
Guangxi
AC C
9
EP
6
10
Shandong
Bayer
1,200
1,600
4,500
11
Guizhou 2
Combined
1,120
1,351
18,750
12,858
15,144
117,707
Total
300 301
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Bayer Henan 3
3,940
16,040
Henan 1
5
870
700
Sintering
4
107
931
Bayer 3
107
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Note: The refineries marked with “*” were in construction at 2011.
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Table 5 Utilization of red mud in China
Red mud
Utilization Methods
Bayer red mud from China local diaspore
Iron & Steel Production
800-1000ktpa
Cement
800-1000 ktpa
Use red mud directly
iron ore separated from red mud
Building materials (bricks)
1000-1300 ktpa
use sand separated from red mud
Rare Earth Elements (REE)
N/A
In research
Polymer filler
10 ktpa
Environmental protection (exhaust gas and waste water adsorbent)
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303
100 ktpa
EP
Total
Glass ceramics, glass fibre…
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All red mud
200-250 ktpa
Note
SC
High iron red mud from gibbsite and diaspore
Building and construction materials
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sintering /combined process
Volume
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302
24
10kt
3000 -3600 ktpa
In pilot research
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Highlights
The characteristics of bauxite residue depend on ores and refining processes. Dry and semi-dry processes in red mud disposal are preferred for environmental and
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safety advantages.
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Utilization of bauxite residue is required to relieve the pressure from disposal.
S0959-6526(14)00668-4
DOI:
10.1016/j.jclepro.2014.06.080
Reference:
JCLP 4475
To appear in:
Journal of Cleaner Production
Received Date: 19 October 2013 Revised Date:
18 May 2014
Accepted Date: 27 June 2014
Please cite this article as: Liu W, Chen X, Li W, Yu Y, Yan K, Environmental Assessment, Management and Utilization of Red Mud in China, Journal of Cleaner Production (2014), doi: 10.1016/ j.jclepro.2014.06.080. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Map of red mud producers location in China
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Environmental Assessment, Management and Utilization of Red
2
Mud in China
3
Wanchao Liu* , Xiangqing Chen, Wangxing Li, Yanfen Yu, Kun Yan
4
Zhengzhou Research Institute of CHALCO, Zhengzhou, Henan, 450041, P.R. China
5
*Corresponding author: Dr. Wanchao Liu
6
Email: [email protected]; Tel/Fax: +86-371-68918623.
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Abstract
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In global alumina production, red mud presents a common problem due to its alkalinity
9
which can contaminate the environment. China is the largest producer both of alumina
10
and red mud in the world. A nationwide investigation was carried out to evaluate the
11
status of residue generation, disposal of and utilization of red mud. Analysis of this
12
study revealed that the characteristics of red mud depend on ore sources and refining
13
processes. Red mud should be categorized as general industrial waste rather than
14
hazardous waste. In China, red mud is considered to be a useful resource rather than a
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contamination. By using contemporary technology, it is possible to utilize 20% of high-iron Bayer red mud and 20% of sintering red mud. More research should be focused on utilization of low-iron Bayer red mud. Keywords
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Red mud, Disposal, Utilization, Investigation, Waste management
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Red mud (Bauxite residue) is a solid waste generated in alumina refining from bauxite.
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It cannot be disposed easily due to its alkali content which can contaminate the
22
environment. Mostly, it is pumped into holding ponds. Red mud presents a problem as
23
it takes up land and can neither be built on nor farmed, even when it has been dry
24
(Rudraswamy and Prakash, 2014). Due to this situation, research has been done to find
25
a suitable way to utilize the mud for other applications.
26
China is the largest producer of both alumina and red mud in the word. In order to get
27
data on the residue generation, disposal and utilization of red mud, a nationwide
28
investigation was carried out by the National Engineering Research Centre for
29
Aluminum Metallurgy and Zhengzhou Research Institute of CHALCO (Aluminum
30
Corporation of China Limited) with the support of the Ministry of Environmental
31
Protection. Part of the investigation results are presented in this paper to offer a
32
reference for international peers in management of red mud.
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1. Alumina Production & Red Mud There are three processes commercially applied for alumina refining, i.e. the sintering process, the Bayer process and the combination process (Bayer-sinter). The sintering
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process was the sole process applied in China before the 1990s because of its high
37
alumina refining ratio from the diaspore bauxite. However, the energy consumption of
38
the sintering processes is much higher than that of two other processes. In 1993, the
39
Bayer process was used in Shandong with imported gibbsite bauxite. The high
40
temperature Bayer process and the flotation Bayer process were also successfully
41
applied with China diaspore bauxite. Presently, the sintering process is mainly used to
42
produce chemical alumina. The sintering process is considered as an important method
43
to refine alumina from low grade bauxite, fly ash and other resources, however, few of
44
these alternatives is applied commercially in China. The alumina product from the
45
sintering process accounts for about 2.5% of total alumina output in 2011.
46
About 3/4 of China alumina capacity is distributed in Henan, Shanxi, Guizhou, Guangxi,
47
Yunnan and Chongqing, because of abundant diaspore deposits in these areas. And the
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rest 1/4 of China alumina capacity is located in Shandong Province because of its
49
region advantage in ocean transport for gibbsite importing. The distribution of alumina
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refineries in China, i.e. red mud producers are shown in Fig.1. Most of the annual alumina production capacities of refineries are over 1 million tonnes per annum.
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2. Characteristics of Red Mud
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2.1 Samples and experimental methods
54
Five kinds of red mud samples were collected for the study from different bauxite and
55
different refining processes (Table 1). These red mud samples are representative in
56
refineries in China and the world. Sample 1, 2, 3 and 4 were generated from Chinese
57
diaspore. Sample 1 and samples 2 were from high temperature digestion Bayer process.
58
And sample 2 has higher iron content than that of sample 1. Sample 3 and sample 4
59
were collected from the combined and the sintering process, respectively. And sample
60
5 was sampled from lower digestion Bayer process and it was generated from gibbsite
61
bauxite imported from Indonesia.
62
For X-ray fluorescence (XRF) analysis of the samples, a sub-sample was melted with
63
1222 flux to produce a flat 40 mm glass tablet for analysis. The tablet was analyzed
64
with a Philips PW 2404 XRF spectrometer.
65
The X-Ray diffraction (XRD) analyses were made on powdered samples in a PANalytical
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multipurpose diffractometer using Co Kα radiation. Phases were identified using XPLOT for Windows and the ICDD database. The specific surface area, pore volume and pore size of samples were tested by the
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automated physisorption and chemisorption analyzer (Autosorb-1-C, Quantachrome
70
Instruments). The fractal dimensions of particles were calculated from the
71
adsorption-desorption data with the Frenkel-Halsey-Hill (FHH) model.
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The corrosivity and toxicity of red mud samples were tested as required by the
73
standards for hazardous properties for hazardous wastes, i.e., Identification standard
74
for hazardous wastes -Identification for corrosivity (Chinese national standard
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GB5085.1-2007) and Identification standard for hazardous wastes - Identification for
76
extraction toxicity (Chinese national standard GB5085.3-2007), respectively.
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2.2 Compositions of red mud
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The characteristics of red mud depend on ore sources and refining processes. The
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chemical composition of the five red mud samples can be found in Table 2. Red mud
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produced from the sintering process and combined process has similar composition
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characteristics (Sample 3 and sample 4). The contents of CaO and SiO2 in the residues
82
from these two processes are much higher than that from the Bayer process. The Fe2O3
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in red mud of Chinese ore (sample 1), except from Guangxi (sample 2) are much lower than that from imported ore (sample 5). The dominating mineral phases in these samples were also studied. The main composition of the red mud from the sintering process is larnite (β-2CaO·SiO2), with a
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mass ratio of over 50%. Dominating mineral compositions in Bayer process red mud are
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desilicification products (DSP), and remaining minerals of bauxite such as hematite,
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quartz etc.. There are different DSP phases in red mud from different ore and digestion
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processes (Fig. 2). When diaspore bauxite is digested in high temperature, quartz is
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reactive. Thus, there is less quartz left in sample 1 and 2, which was generated from
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diaspore, than that in sample 5, which was generated from gibbsite. To decrease the
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aluminum loss in DSP caused by more reactive silicon, lime is added into the diaspore
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slurry. So in sample 1 and 2, most of DSP phases are cancrinite and hydrogarnet, as well
95
as natrodavyne.
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From view of composition, red mud in China could be classified into 4 kinds, i.e.,
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sintering process red mud, lower iron diaspore red mud from Bayer process, high iron
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diaspore red mud from Bayer process, gibbsite red mud. The proportions of 4 kinds of
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red mud in China in 2011 are shown in Fig.3. The products of red mud are calculated
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from alumina product and red mud generation ratios in related processes. As shown in
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Fig.3, 7% of red mud is generated from sintering process, 26% of red mud is generated from imported gibbsite, and 67% of red mud is generated from the Bayer process with local diaspore including 49% from low iron bauxite and 18% from high bauxite.
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2. 3 Particle Properties
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Red mud is an aggregate of particles with different fineness. Research shows that the
106
specific surface areas and pore characteristics of red mud are also different because of
107
bauxite ore and refining processes (Table 2). The specific surface area of red mud
108
becomes larger with higher pore volume and smaller with average pore size.
109
Particularly, the specific surface area of red mud from gibbsite is much larger than
110
other samples, the reason for this may be the easy digestion properties of gibbsite
111
from bauxite, which forms tiny channels in red mud particles. The difference between
112
sample 1 and sample 2 is possibly caused by the relatively hard hematite particles in
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sample 2. In the sintered red mud, an amount of molten phase is generated which
114
leads to higher density and smaller specific surface area. The fractal dimensions of
115
particles
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Frenkel-Halsey-Hill (FHH) model. The data quantifies the structural characteristics of
117
the red mud particles. From the data, fractal dimension (D) of samples are varying
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calculated
from
the
adsorption-desorption
data
with
the
EP
was
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between 2.75 - 2.82, which show that red mud particles are fractal. Sample 4 is revealed to be coarser than others. 2.4 Environmental Properties "Hazardous waste" is a category designated by the Basel Convention on the Control of
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Trans boundary Movements of Hazardous Wastes and Their Disposal for substances
123
which possess one or more hazardous properties, i.e. corrosivity, toxicity, ignitability,
124
reactivity and/or infectivity. From common sense reasoning, the ignitability of red mud
125
is poor, and the reactivity and infectivity of red mud are weaker than that of hazardous
126
materials. The corrosivity and toxicity test results from the red mud samples show that
127
(Table 3) the pH values of samples are lower than corrosivity limit (12.5) and the toxic
128
element contents of samples are lower than toxicity limits. Thus these red mud
129
samples are general industrial waste but not hazardous waste. Red mud is not
130
categorized as a hazardous material in the Chinese National Catalogue of Hazardous
131
Wastes (2008), which is issued by the Chinese government to reinforce the
132
management of hazardous waste.
133
After the Ajka tragedy in Hungary, public attention was focused on the environmental
134
properties of red mud. The Hungarian government stated that the mud is not
135
poisonous (Government of Hungary, 2010), and the Hungarian Academy of Sciences
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stated that the heavy metal concentrations were not considered dangerous for the environment. This opinion was also supported by Enserink (2010). What should be mentioned here is that, the pH of red mud supernatant liquor usually is 12-14, which is hazardous to the surrounding ecology. It is believed that the main
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damages in the Ajka accident caused first by arose from the high pH of the mud slurry,
141
which was responsible for both severe chemical burns to humans and animals and
142
killing specimens in the rivers and contaminated soils. In order to safely dispose of red
143
mud, it is crucial to wash, dewater, and neutralize before it is discharged.
144
3. Disposal of red mud in China
145
Investigation of disposal data was obtained from 11 alumina plants (in operation or in
146
construction). The total alumina capacity of these 11 plants is 12.858 million tonnes
147
per year (Table 4), which is about 30% of national alumina capacity. The data gathered
148
from the 11 plants was used to estimate the generation ratios of red mud from
149
different processes. It can be predicted that, until the end of 2011, there are 250
150
million tonnes of red mud in over 60 storage sites on 25 km2 land in China.
151
Until the end of 2011, in these 11 refineries, there are 14 available red mud storages, 5
152
closed storages and 10 storages in planning or construction stage. From the obtained
153
data, wet disposal technology is applied the most widely. In the 19 old storages, which
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are in using or closed, only 3 storages applied dry or semi-dry processes. Due to the environmental and safety factors it is a trend to apply dry and semi-dry processes in new sites. In the 10 sites which are in construction or in planning, 3 of them will use
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dry process, and 2 will use the semi-dry process; the other 5 sites will apply the wet
158
disposal technology because of local ravine terrain.
159
Most of the disposal sites of the 11 alumina plant are being operated normally as
160
required by a series of laws and regulations issued on management of red mud and
161
general waste. However, few closed red mud storages were ecologically restored as
162
required. The reclamation of the storages should be stressed in the future to decrease
163
the environmental impact of red mud.
164
Red mud is characterized as alkalinity, high moisture content and poor cementing
165
properties, that is different from other industrial wastes. For normalization of red mud
166
disposal storage designing, the Design Code of Red Mud Storage Pond with Dry Process
167
is being drafted by specialist agencies. All of the procedures concerned in the dry
168
disposal of red mud will be normalized in the code from site selection, designing,
169
damming, seepage-proofing, flood drainage, water backing, residue transporting,
170
operation management, to safety monitoring.
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4. Utilization of Red Mud The utilization of red mud as a second resource can be useful to reduce management cost. It is one of the objectives of the government of China to utilize 20% of fresh red
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mud by the end of 2015 (MIIT and MOST, 2010). Substantial research and field
175
applications have been carried out in this field (Wanchao et al., 2009a). The status of
176
red mud utilization technologies are shown in Table 5.
177
The red mud from the sintering or combined process is pozzolanic, so it is useful in
178
producing building and construction material. Around 10 million tonnes of red mud
179
were used in Portland cement production commercially. However, it was terminated
180
due to the new cement standard which increased the limitation of Na2O+K2O content
181
because of alkali-aggregate reaction (Tongsheng et al, 2013). The Shandong Branch of
182
CHALCO built a pilot plant for non-sintering brick production using the red mud from
183
sintering process (Jiakuan and Bo, 2008). The quality of bricks was found to satisfy the
184
local building material requirements, but the efflorescence is the biggest hurdle to high
185
quantity addition of red mud in building materials. A demonstrated road 4 km long was
186
built with red mud road base material. The application of red mud in road building
187
depends on the distance between the refinery and the road construction sites, because
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the consumer does not want to pay high transporting cost. Every year, 150-200 kt sintering red mud is used in building material production and construction. Over 50 ktpa of red mud from sintering and combination process was used to build the red mud dams and the qualities of dams are satisfying.
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A plant has been in operation to produce glass-ceramics with red mud in Shanxi from
193
2013. About 10 kt red mud will be consumed annually in 450,000 m2 glass-ceramics
194
production. The red mud which is used in the plant is produced by sintering process
195
from local diaspore bauxite.
196
For the residue from the Bayer process which has high iron content, iron concentrating
197
is carried out. The process is applied in several plants which are fed with local high iron
198
bauxite and imported bauxite from Indonesia, Australia and Fiji. The physical process
199
works well in iron recovery from red mud. The bauxite residue was separated into
200
three parts, i.e., the iron ore, sand and fine mud and was accomplished through
201
cyclone separator, magnetic separator, spiral chute and shaking table sequentially. The
202
total Fe2O3 content in the concentrate varies from 50-70%. The sand was used as a raw
203
material in concrete bricks. The economic assessment showed that the process is
204
viable. From 2010, around 10 million tonnes of the residue were treated and at least
205
80-100 kt of iron ore was concentrated annually. The concentrate is used in iron and
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steel production and cement production. The high temperature reduction of hematite to magnetite or metallic iron was also carried out in lab to improve the concentrate levels and the recovery rate (Wanchao et al., 2009b, 2012). Based on the fine particle size, a filler can be produced from raw red mud and the
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tailings of iron ore separation from red mud. The filler can be used in polymer products.
211
The technology is applicable to all kinds of red mud. Unfortunately, the market
212
requirement for the filler is too small compared with the production of red mud.
213
In order to use the lower iron red mud, recovery of rare earth elements (Dongyan &
214
Chuansheng, 2012), and adsorption of heavy metal from contaminated water (Yi et al,
215
2010) and acid from gas (Hongtao et al, 2013) are also being researched. However,
216
these processes are not yet commercially applicable until now because of economic or
217
engineering reasons. For example, HCl is applied in rare elements extraction from red
218
mud in present technologies. So equipment cost on the extraction is high because most
219
of equipment should be preservative treated. When red mud is used for heavy metals
220
adsorption, more residues will be generated than common adsorbents. The
221
desulfurization system cannot run for long term stably due to serious scaling caused by
222
red mud desulfurizer.
223
From our present technological status, it is possible to utilize 20% of high-iron Bayer
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red mud and 20% of sintering red mud. But in China, there is 49% of red mud from Bayer process with lower iron diaspore. Red mud utilization is still a challenge for China.
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5. Conclusions
228
The characteristics of red mud depend on ore sources and refining processes. Generally,
229
red mud should be categorized as general industrial waste rather than hazardous waste.
230
The dry disposal process and the semi-dry disposal process should be encouraged or
231
even be driven by legislative compliance to be applied in more plants. The dewatering,
232
soda recovery, neutralization and ecological restoration should be emphasized due to
233
environmental safety. Great progresses are being obtained in China on red mud
234
treatment. By using contemporary technology, it is possible to utilize 20% of high-iron
235
Bayer red mud and 20% of sintering red mud. However, more research should be
236
focused on utilization of low-iron Bayer red mud.
237
As well as China, the treatment of red mud is still a challenge to global alumina industry.
238
Open atmospheres about the treatment and utilization of red mud should be built both
239
in China and in the international community.
240
Acknowledgement
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Authors would like to acknowledge the funding of the China Ministry of Environmental Protection (No. 1441100023) and National Natural Science Foundation of China (Grant No. 51304216).
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244 Reference
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Dongyan L., Chuansheng W. (2012). Stockpiling and Comprehensive Utilization of Red Mud Research
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Progress. Materials, 5, 1232-246.
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Enserink M. (2010). After red mud flood, scientists try to halt wave of fear and rumors. Sci., 330:
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432–433.
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Government
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http://redsludge.bm.hu/?p=59#more-59.
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Hongtao L., Kuihua H., Shengli N., Chunmei L., Mengqi L., Hui L. (2013). Experimental study and
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mechanism analysis of modified limestone by red mud for improving desulfurization. Cleaner
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Combustion and Sustainable World. DOI:10.1007/978-3-642-30445-3_65.
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Jiakuan Y., Bo X. (2008). Development of unsintered construction materials from red mud wastes
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produced in the sintering alumina process. Const. Buil. Mat., 22: 2299 - 307.
257
Ministry of Industry and Information Technology (MIIT), and Ministry of Science and Technology
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(MOST),
259
http://www.miit.gov.cn/n11293472/n11293832/n12843926/n13917027/14011841.html
260
Rudraswamy M.P., Prakash K. B. (2014). An experimental investigation on the effect of alternation of
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Red
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Guidance
on
sludge
and
detoxification.
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(2010).
Comprehensive
Utilization
of
Red
Mud.
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(2010).
Hungary
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of
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alternate wetting and dry on the properties of concrete produced by red mud. Int. J. Advanced
Research, 2(1): 473-484.
Yi L., Yetang H., Duojun W., Yongxuan Z. (2010). Effect of red mud on the mobility of heavy metals in
mining-contaminated soils. Chinese J. Geochemistry, 29(2): 191-196.
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Tongsheng Z., Peng G, Pinhai G., Jiangxiong W., Qijun Y. (2013). Effectiveness of novel and traditional
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methods to incorporate industrial wastes in cementitious materials—An overview. Res. Cons.
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Recycl., 74: 134-143
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Wanchao L., Jiakuan Y., Xiao B. (2009a). Review on treatment and utilization of bauxite residues in
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China. Int. J. Mineral Proc., 93, 220-231.
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Wanchao L., Jiakuan Y., Bo X. (2009b). Application of Bayer red mud for iron recovery and building
271
material production from alumosilicate residues. J. Hazard. Mat., 161: 474 - 478.
272
Wanchao L., Shouyi S., Ling Z., Sharif J., Jiakuan Y. (2012). Experimental and simulative study on
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phase transformation in Bayer red mud soda-lime roasting system and recovery of Al, Na and Fe.
274
Min. Eng., 39: 213-218.
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Fig.1 Map of red mud producers location in China
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1, Natrodavyne; 2, Cancrinite; 3, Calcite; 4, gibbsite;
284
5, Diaspore; 6, Hematite; 7, Al(OH)3; 8, Alumogoethite; 9, Quartz; 10, Hydrogarnet.
285
Fig.2 XRD patterns of Bayer red mud samples
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287 High iron diaspore red mud from Bayer process, 18%
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Red mud from sintering and combined process, 7%
High iron gibbsite red mud from Bayer process, 26%
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Fig.3 Proportion of 4 kinds of red mud in China (2011)
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Low iron diaspore red mud from Bayer process, 49%
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Sample No.
1
Fed bauxites
diaspore
Bauxite origin
Henan, China
Processes
Bayer
Bayer
Digestion temperature
260oC
260oC
3
4
5
diaspore
gibbsite
Shandong, China
Indonesia
Combined
Sintering
Bayer
N/A
N/A
140 oC
diaspore Shanxi, China
M AN U
diaspore (high iron) Guangxi, China
AC C
EP
TE D
292
2
RI PT
Table 1 Red mud samples from different refiners
SC
291
20
ACCEPTED MANUSCRIPT
1
2
3
4
5
Al2O3, %
25.48
18.87
10.5
8.32
17.85
SiO2, %
20.58
8.87
22.2
32.5
20.48
Fe2O3, %
11.77
34.25
6.75
5.7
32.14
TiO2, %
4.14
6.05
2.55
/
3.57
K2O, %
2.07
0.08
0.85
/
/
Na2O, %
6.55
4.35
3.00
2.33
6.75
CaO, %
13.97
13.59
42.25
41.62
8.21
MgO, %
1.54
0.41
2.46
/
/
M AN U
SC
Samples
11.65
7.37
5.31
/
30.72
Pore volume, ×10-3cm3/g
11.15
7.05
4.75
/
22.94
Average pore size, nm
3.83
3.82
3.58
/
2.99
Fractal dimension
2.75
2.75
2.78
/
2.82
EP
Specific surface area,m2/g
AC C
294 295
RI PT
Table 2 Chemical & physical characteristics of red mud from different refiners
TE D
293
Note: “/” means the datum was not tested.
21
ACCEPTED MANUSCRIPT
Table 3 Testing results for corrosivity and extraction toxicity of bauxite residue
Unit pH (corrosivity)
1
2
3
11.33
10.66
12.18
5
Limits*
9.77
<12.5
<0.05
5
1.14
100
RI PT
296
mg/L
0.23
0.21
<0.05
F-
mg/L
2.03
2.03
0.18
CN-
mg/L
0.91
0.91
0.26
0.2
5
Total Ag
mg/L
<0.01
<0.01
<0.01
<0.01
5
As
mg/L
<0.1
<0.1
<0.1
<0.1
5
Ba
mg/L
<0.003
<0.003
<0.003
<0.003
100
Be
mg/L
<0.0003
<0.0003
<0.0003
<0.0003
0.02
Cd
mg/L
<0.003
<0.003
<0.003
<0.003
1
Cr
mg/L
0.16
0.12
<0.01
<0.01
15
Cu
mg/L
<0.01
<0.01
0.027
0.015
100
Ni
mg/L
Pb
mg/L
Se
mg/L
Zn
mg/L
M AN U
TE D
<0.01
<0.01
<0.01
5
<0.05
<0.05
<0.05
<0.05
5
<0.5
<0.5
<0.5
<0.5
1
<0.006
<0.006
<0.006
<0.006
100
<0.0005
<0.0005
<0.0005
0.1
EP
<0.01
mg/L
<0.0005
297
*: The limits of hazardous properties are reference to Identification standard for hazardous wastes
298
AC C
Total Hg
SC
Cr6+
(GB5085.1-7, 2007).
22
ACCEPTED MANUSCRIPT
Table 4 alumina and red mud disposal data from 11 alumina plants
RI PT
299
Total amount of red
Processes
Alumina
Red mud
used in the
production in
production in
refinery
2010, kt
2010, kt
mud produced up
Refineries No. location
until the end of 2010,
Guizhou 1
2
Shanxi 1
Bayer
74
Bayer
860
Combined
1,860
3,080
18,690
80
280
11,000
750
850
20,650
950
934
3,500
Bayer
810
1,215
3,210
Bayer
20,00
2,600
7,500
Bayer*
0
0
0
Bayer
173
97
300
Sintering*
0
0
0
Bayer
2,050
1,460
9,520
Sintering Henan 2
Shanxi 2
7
Chongqing 1
8
Chongqing 2
Guangxi
AC C
9
EP
6
10
Shandong
Bayer
1,200
1,600
4,500
11
Guizhou 2
Combined
1,120
1,351
18,750
12,858
15,144
117,707
Total
300 301
TE D
Bayer Henan 3
3,940
16,040
Henan 1
5
870
700
Sintering
4
107
931
Bayer 3
107
M AN U
1
SC
kt
Note: The refineries marked with “*” were in construction at 2011.
23
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Table 5 Utilization of red mud in China
Red mud
Utilization Methods
Bayer red mud from China local diaspore
Iron & Steel Production
800-1000ktpa
Cement
800-1000 ktpa
Use red mud directly
iron ore separated from red mud
Building materials (bricks)
1000-1300 ktpa
use sand separated from red mud
Rare Earth Elements (REE)
N/A
In research
Polymer filler
10 ktpa
Environmental protection (exhaust gas and waste water adsorbent)
AC C
303
100 ktpa
EP
Total
Glass ceramics, glass fibre…
TE D
All red mud
200-250 ktpa
Note
SC
High iron red mud from gibbsite and diaspore
Building and construction materials
M AN U
sintering /combined process
Volume
RI PT
302
24
10kt
3000 -3600 ktpa
In pilot research
ACCEPTED MANUSCRIPT
Highlights
The characteristics of bauxite residue depend on ores and refining processes. Dry and semi-dry processes in red mud disposal are preferred for environmental and
RI PT
safety advantages.
AC C
EP
TE D
M AN U
SC
Utilization of bauxite residue is required to relieve the pressure from disposal.