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Using strong acid–cation exchange resin to reduce potassium level in molasses vinasses
Desalination 286 (2012) 210–216
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Using strong acid–cation exchange resin to reduce potassium level in molasses vinasses Ping-Jun Zhang, Zhen-Gang Zhao, Shu-Juan Yu ⁎, Yong-Guang Guan, Dan Li, Xiang He College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, China Guangdong Province Key Laboratory for Green Processing of Natural Products and Product Safety, South China University of Technology, Guangzhou 510640, China
a r t i c l e
i n f o
Article history: Received 12 July 2011 Received in revised form 25 October 2011 Accepted 9 November 2011 Available online 15 December 2011 Keywords: Molasses vinasse Desalting Potassium Ion-exchange
a b s t r a c t Molasses-based distilleries are one of the most vulnerable to pollution industries, which always generate large volumes of high strength vinasse. Recently, one of the most effective re-applications/reuse of vinasse is concentrating the molasses vinasse to prepare as fodder additive for animal food. However, the dosage of molasses vinasse to be added as animal feed is always limited because of the unexpectedly high potassium content in molasses vinasse. In present study, potassium ions were firstly extracted from molasses vinasses using a strong acid–cation exchange resin, and then desorbed from the resin and dissolved into the eluate by H2SO4 solution as the strong acid–cation exchange resin was regenerated. Finally, evaluation to recycle and reuse the mother liquor (once-used eluant), after extracting K2SO4 crystals from the eluant, was investigated. Results indicated that using the mother liquor to elute the resin column which absorbing K+ from molasses vinasse was a potential means for industrial production of potassium salt. Meanwhile, the molasses vinasse which has removed most potassium ions might be used as animal feed. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Molasses vinasse is the remain of the fermentation and distillation of alcohol from cane and beet molasses [1]. On an average 8–15 L of effluent is generated for every liter of alcohol produced [2]. On the other hand, the molasses vinasse is extensively growing due to widespread industrial applications of alcohol such as in pharmaceuticals, food, perfumery, fuel, etc. [3]. The effluent always has a high level of organic content such as crude proteins, lactic acid, glycerol, cholesterol, amino acid and reducing sugars (COD in the range of 80,000–100,000 mg/L and BOD in the range of 40,000–50,000 mg/L), strong odor and dark brown color [4–7], and it also contains nutrients in the form of nitrogen (1660–4200 mg/L), phosphorus (225– 3038 mg/L) and potassium (9600–17,475 mg/L) [8–10], which have resulted in serious environmental problems, such as eutrophication of bays, lakes, and inland seas. However, in addition to pollution, increasingly stringent environmental regulations are forcing distilleries to improve existing treatment and also explore alternative methods of effluent management [5]. Recently, many research teams focused on the study of preparing nutriment fodder using molasses vinasses. However, the dosage of molasses vinasses was also limited, because unexpectedly high potassium content in molasses vinasse could lead to bulls and pigs diarrhea [7,11–13]. The removal of potassium from molasses vinasse has been ⁎ Corresponding author at: #381, Wushan road, Guangzhou, China. Tel./fax: + 86 20 87113668. E-mail address: [email protected] (S.-J. Yu). 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.11.024
widely investigated, and various techniques proposed for its removal, such as chemical precipitation, electrodialysis, reverse osmosis and ion exchange. Of these processes, chemical precipitation, electrodialysis and reverse osmosis have been widely used for the treatment of potassium in molasses vinasse [4,13–19]; however, these techniques are expensive, and require complex and strict control of the operating conditions. Conversely, ion exchange technique is easy to operate and allows the potassium to be recycled. The successful accomplishment of this technique depends on the choice of an adequate eluant and routing. The study aims to fully reduce potassium level in molasses vinasses by using strong acid–cation exchange resin (ZGC 108). Firstly, we chose acids which were representative of groups commonly found in market. Potassium ions were then extracted from molasses vinasses using a strong acid–cation exchange resin, and desorbed from the resin and dissolved into the eluate during the resin regeneration process using chosen acid solution. Finally, the reused of mother liquor (as part of the eluant for the next cycle), which is the eluate after extracting of potassium salt by crystallization, to more fully utilize the remaining H + was investigated. 2. Materials and methods 2.1. Experimental materials and main apparatus ZGC108 ion exchange resin (Na + form) (Hangzhou Zheng Guang Co., Ltd, China) was used to extract K + from sugarcane molasses vinasse (Zhongneng Ethanol Co., Ltd, China). All the chemicals used
P.-J. Zhang et al. / Desalination 286 (2012) 210–216
were analytical pure and purchased from Guangzhou Chemical Co., Ltd. (Guangzhou, China). In this experiment, main equipments and their application were shown as follows. A flame photometer (FP640, Aimusheng of Shanghai Co., Ltd, China) was used for potassium analysis [20,21]. A constant flow pump (HL-200B, Jingke Shiye of Shanghai Co., Ltd, China) was used to provide a stable flow velocity of leacheate. A thermostatic water bath (Pudong Rongfeng of Shanghai Co., Ltd, China) was provided for the stabilization of temperature. A reactor (total volume, 1 L) (Asahi Seisakusho Inc, Japan) with a stirrer (IKA, Internet Khazak Alippe GmbH & Co, Germany) and a programmable cooling & heating controller (CC2, Huber Kältemaschinenbau GmbH, Germany) was used to produce potassium sulfate crystals. A conductivity meter (DDS-11A, Leici Xinjing of Shanghai Co., Ltd, China) was used for the conductivity measurement of distilled water. The ion exchange columns were made to our specifications by a glass apparatus company (Guangzhou Tianhe Precision Instruments Wholesale Division of the Department of Glass Co. LTD). 2.2. Selection of eluents Four considered acids were evaluated for elution capacity of K + on the resin. First, four 50 mL of the wet resin in the K + form were added to 4 flasks containing 250 ml of a labeled 0.3 mol/L H2SO4, 0.6 mol/L HCl, 0.2 mol/L H3PO4 and 0.6 mol/L CH3COOH, respectively, water solution. The flasks were maintained at a temperature of 35 °C and agitated (50 rpm) in a thermostatic water bath. Hourly samples (5 ml) were taken for K + analysis until the concentration was unchanged. The desorption capacity of K + was calculated per wet volume of resin according to the determined data. 2.3. Experimental routings and methods A schematic drawing of ion-exchange experimental facilities was shown in Fig. 1a. It was performed in three glass columns, #a (2.6 cm internal diameter and 10 cm length), #b and #c (3.3 cm internal diameter and 30 cm length). Firstly, the #a column was packed with 50 mL quartz sand with particle size distribution of 0.05– 0.20 mm, then, washed using distilled water until the conductivity of the effluent was lower than 2μS/cm. At last, both #b and #c columns were filled with 180 mL wet-settled bed volume (BV) of resin, respectively. The column adsorption experiments were carried out by three routing (#A, #B and #C routing). In the #A routing, the 3, 5, 6, 8, 10, 11 valves were closed while the 1, 2, 4, 7, 9, 12 valves were opened. The #a, #b and #c columns were connected in series, respectively. Molasses vinasse was down flowed from #a to #b, and then to #c columns. In the #B routing, the 3, 4, 7, 8, 9, 12 valves were closed while the 1, 2, 5, 6, 10, 11 valves were opened. The #a, #b and #c columns were connected in series, respectively. Molasses vinasse which was down flowed from #a, was up flowed past #b and then past #c columns. In the #C routing, two steps were carried out. First, the 3, 6, 7, 10, 11 valves were closed while the 1, 2, 4, 5, 8, 9, 12 valves were opened. The #b and #c were concurrent flow, both #b and #c were connected with the exit of #a. 1620 mL, i.e. 4.5BV, molasses vinasse which was down flowed from #a column, was then down flowed equally past #b and #c columns. Second, after the first step was carried out, the 3, 5, 6, 8, 10, 11 valves were closed while the 1, 2, 4, 7, 9, 12 valves were opened. The #a, #b and #c columns were connected in series. Molasses vinasse was down flowed past #a, #b, and #c columns in tandem. The molasses vinasse was flowed past the columns at a flow rate of 360 mL/h (1BV/h) using a constant flow pump. Each successive 100 mL fractions of the effluent were collected using a fraction
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collector. Breakthrough curves were obtained by analyzing each fraction using a flame photometer. The column elution experiments were carried out using two routing (#D and #E routing). In the #D routing, the 1, 2, 5, 6, 8, 10, 11 valves were closed and the 3, 4, 7, 9, 12 valves were opened. The #b and #c columns were connected in series. Sulfuric acid solution with different concentrations, 0.2 to 0.6 mol/L, was down flowed past #b and #c columns in tandem. In the #E routing, two steps were carried out. First, the 1, 2, 6, 7, 10, 11 valves were closed while the 3, 4, 5, 8, 9, 12 valves were opened. The #b and #c were concurrent flow. Sulfuric acid solution was down flowed equally past #b and #c columns at a flow rate of 1080 mL/h, i.e. 3BV/h, at 35 °C. Second, after the first step was carried out, the 1, 2, 5, 6, 8, 10, 11 valves were closed and the 3, 4, 7, 9, 12 valves were opened. The #b and #c columns were connected in series. Sulfuric acid solution was down flowed past #b and #c columns in tandem at a flow rate of 1080 mL/h, i.e. 3BV/h, at 35 °C. The different concentration of sulfuric acid solutions were used for column elution as the flow rate of 3BV/h (1080 mL/h) at 35 °C. The elution was completed as the concentration of potassium ions in the elution solution was lower than 0.01 g/L.
2.4. Resin pretreatment The ion-exchange resin that was pretreated as follows. The resin ZGC108 was soaked with distilled water in round glass container for 24 h, and then, treated with 1 mol/L NaOH solution (triple resin volume) and then 1 mol/L HCl solution (triple resin volume) for 6 h, respectively. Finally, the resin was washed with distilled water until the pH of the wash water was about 6.5. After the pretreatment in this experiment, the functional sites on resin were changed from Na + form to H + form [22].
2.5. Chemical analysis 2.5.1. Determination of K + K + in the sample was determined by flame photometer [21,23]. Sample was diluted some fold for the K + determination. Standard solutions of two different concentrations were used for calibration: 20 μg K +/mL and 80 μg K +/mL.
2.5.2. Determination of H + The concentration of H + in the solution was determined using a chemical titration method. A 10.0 mL sample of solution was shaken with 30.0 mL of distilled water and 1 mL of phenolphthalein solution (0.5 g/L). Then the mixture was titrated with a 0.100 mol/L NaOH solution from colourless to just red colorimetric endpoint with the volume of titrant used recorded as V mL. The concentration of H + in the solution was calculated as 0.100× V/10.0, in mol/L.
2.5.3. Determination of multivalent cations The concentration of multivalent cations, such as Ca 2+ and Mg 2+ etc. in the molasses vinasse was determined using a chemical titration method. A 5 mL sample of molasses vinasse was shaken with 95 ml of distilled water, 5–15 mL of ammonia buffer (pH 10.0–13.0) and 0.1 g of eriochrome black T (EBT) which is a complexometric indicator that is part of the complexometric titrations. Then the mixture was titrated with a 3.57 mmol/L EDTA–Na2 solution from purple to blue colorimetric endpoint, with the volume of titrant used recorded as V, in mL. The concentration of multivalent cations in the molasses vinasse was calculated as 3.57 × V/5.0, in mmol/L.
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Fig. 1. Schematic drawing of experimental setup and process: (a) Fixed-bed ion exchange column system; (b) K2SO4 crystallization experimental setup; and (c) Recovery process.
2.6. Computing methods Sorption capacity of the resin (q; mg/mL) was calculated based on Eq. (1) [22,24]. Vt
q ¼ ∫0
C 0 −CÞdV V′
ð1Þ
where, V’ (mL), Co (mg/mL), C (mg/mL) and Vt (mL) were the volume of the ion-exchange resin, the initial potassium concentration,
the effluent potassium concentration and the effluent volume(V) as a function of time (t), respectively. The K + in the resin elution rate (Q; %, w/w) was calculated based on Eq. (2). Q¼
ab 100% c
ð2Þ
where, a (mg/mL), b (mL) and c (mg) means the potassium concentration in the eluent, the total eluent volume and the sorption capacity of the resin in the columns, respectively.
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The H + in the H2SO4 eluate utilization rate (N; %, w/w) was calculated based on Eq. (3). N¼
de 100% f g
Table 2 Adsorption capacity of the resin (ZGC 108) for K+ at three routings. Item
Breakthrough volume (mL)
Breakthrough capacity (mg/mL)
Saturated volume (mL)
Saturated capacity (mg/mL)
#A #B #C
2000 1910 2065
54.07 52.84 56.79
2410 2460 2330
65.81 65.96 66.58
ð3Þ
where, d (mol/L), e (L), f (mol/L) and g (L) means the H + concentration in the total eluant, the total eluant volume, the H + concentration in the total eluent and the total eluent volume, respectively. 3. Results and discussion 3.1. Choice of the acid Compared on the basis of acids performance in desorption K + from the resin, the acids (H2SO4, HCl, H3PO4 and CH3COOH, respectively) treatment of the resin was introduced. Table 1 shows that the acids are evident demonstrating highest K + desorption capacity H2SO4 and HCl at 45.5 and 47.0 mg K +/ml wet resin, respectively. Of these two, the HCl acid has a little higher desorption quantity than H2SO4 acid. In general, acid in a strong acid form can desorb more K + from strong acid–cation exchange resin (ZGC108) than those acids in a mediate strong acid (H3PO4) or weak acid(CH3COOH) at 18.5 and 8.2 mg K +/ml wet resin, respectively, which may be explained by law of mass action [25]. Under the testing conditions, the H ions in strong acid are easier di ociation than that in mediate strong or weak acid. Therefore, on the same conditions, acid (H2SO4 and HCl) in strong acid form is more suitable to desorb K + on the resin than in mediate strong (H3PO4) or weak (CH3COOH) acid form. In practice, acid HCl is a volatile acid, and it is not suitable to be reused. Based on these considerations, acid H2SO4 was selected as the acid with which to continue the study of eluting K + on the resin.
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among three routings, the least breakthrough exchange capacity value was the #B routing (see Table 2), which may be explained by back diffusion. Under the #B routing testing conditions, the back diffusion velocity of the K + in upflow molasses vinasse was faster than K + in downflow molasses vinasse, Therefore, the #B routing wasn't suitable to desalting the K + in the molasses vinasse, and the back diffusion between the molasses vinasse containing K + and the molasses vinasse without K + played a significant role on the column performance. However, using the #C routing that might avoid the drawback of the #A and #B routing and got satisfied breakthrough exchange capacity, and, in general, 6–7 h of adsorption time was suitable for an ion exchange operation unit for economic reasons. Then, at the same condition, experiments using the #C routing were carried out in triplicates. Means and standard deviations of the data were calculated for each treatment. Analysis of variance (ANOVA) was carried out to determine any significant differences among the applied treatments by the SPSS package (SPSS 10.0 for windows), and the equilibrium saturated exchange capacity was constant, about 56.78 mg K +/ mL wet resin(P b 0.05). Based on these considerations, the #C routing was selected as the adsorption routing with which to continue the study of elution condition.
3.3. Changes of H2SO4 concentration 3.2. Changes of exchange routing
1.0 A B C
0.8
0.6
C/C0
In order to select the most suitable routing for desalting, three routings (#A, #B and #C, respectively) which detailed in Section 2.3 (Experimental routings and methods) were recommended to adsorb K + from sugarcane molasses vinasse and the different routings schematic diagram was shown in Fig. 1a. The condition for carrying out ion exchange was (1) concentration 9.9 mg K +/mL, (2) pH of influent 4.0, (3) temperature 28 °C, (4) flow rate 1BV/h (360 mL/hr). In Table 2, the #A, #B, and #C routing indicated higher K + saturated exchange capacity at 65.81, 65.96 and 66.58 mg K +/mL wet resin, respectively. And the profiles of breakthrough curves were shown in Fig. 2 that demonstrated the breakthrough exchange ability of the ZGC108 resin, based on the ratios of the areas under curves from C/ Co = 0 to C/Co = 1. The #C routing got a higher breakthrough exchange capacity (56.79 mg K +/mL wet resin) than #A or #B routing (54.07 and 52.84 mg K +/mL wet resin, respectively). Some discussions were detailed as follows. Firstly, the K + in the molasses vinasse was exchanged completely by activation of functional sites on the #b column resin in the beginning stage, then, the pores of resin in the #c column was clogged by some bigger molecules in sugarcane molasses vinasse, resulting in lower breakthrough exchange capacity values of the resin, which was detected as the #A routing was on. Moreover,
The aim of this test was to elute the K + on the functional sites of the resin with H2SO4 solution. The advantage was that the extraction of K + and regeneration of resin took place simultaneously, because the functional group of the resin was changed from K + to H + form in a single desorption process using H2SO4 solution as eluent. The K + in five groups exchange equilibrated resin were adsorbed using the #C routing, then the K + on the resin were eluted using the #D routing (detailed in Section 2.3. Experimental routings and methods) by 6 BV H2SO4 solution at a flow rate of 3BV/h with 35 °C, and the concentrations of H2SO4 eluant solution were 0.6, 0.5, 0.4, 0.3 and 0.2 mol/L, respectively.
0.4
0.2 Table 1 Desorption capacity of K+ on the resin using different acids.
0.0 Acids
Concentration (mol/L)
Specific desorption capacity (mg K+/ml wet resin)
H2SO4 HCl H3PO4 CH3COOH
0.3 0.6 0.2 0.6
45.5 47.0 18.5 8.2
1400
1600
1800
2000
2200
2400
2600
2800
V/mL Fig. 2. Breakthrough curves for the removal of potassium by the resin ZGC 108 at three routings.
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30
Table 3 The K+ elution rate and H+ utilization rate as a function of H2SO4 concentrations. Elution volume (BV)
K+ elution H+ rate (%) utilization rate (%)
Phenomena
0.6
6
99.6
22.3
0.5
6
99.7
26.7
0.4
6
99.6
32.8
0.3
6
93.4
42.1
0.2
6
86.8
59.3
Many crystals in the middle of #b column, several in #c column. Some crystals on the bottom of #b column, many on the top and middle part of #c column. No crystals in the #b column, but several in the middle and lower part of #c column. No crystals in the #b and #c column. No crystals in the #b and #c column.
K+ conceration (g/L)
25
H2SO4 concentration (mol/L)
D1 D2 D3
20 15 10 5 0 0
1
2
3
4
5
6
7
Eluate volume (mL/mL resin) Table 3 shows the effects of different H2SO4 concentration eluant on desorption of the K + on the resin by batch treatment. As shown in Table 3, about 99.6% of the K + on the resin was desorbed when the operating H2SO4 concentration from 0.4 to 0.6 mol/L. The K + elution rate was increased from 86.8 to 99.6% when the H2SO4 concentration ranged from 0.2 to 0.4 mol/L. The reason for the lower desorption rate in the H2SO4 concentration at 0.2 and 0.3 mol/L may be related to the activity coefficient of H ions in the eluent [25]. According to the data in Table 3 inferred that the activity coefficient of H ions in water solutions increased along with the increase in the H2SO4 concentration between 0.2 and 0.4 mol/L, while the activity coefficient of H ions didn't changed between 0.4 and 0.6 mol/L. A similar finding was detailed by Staples et al., (1981) and Michelsen et al., (1998), who indirectly confirmed that the activity coefficient of H ions in water solution was connected with H2SO4 concentration [26,27]. As expected, the H + utilization rate decreased from 59.3 to 22.3% w/w with the concentration of H2SO4 changed from 0.2 to 0.6 mol/L (see Table 3). On the other hand, an interesting phenomenon that some crystals appeared in the columns (#b and #c columns) was observed with the H2SO4 concentration between 0.5 and 0.6 mol/L (see Table 3). The maximum level of K + in eluate was 0.705 mol/L (27.5 g K +/L) at 35 °C, and, according to the literature [28], the solubility of K2SO4 was about 0.706 mol/L at the same temperature. It could be inferred that there was no K2SO4 crystal in eluate in this condition. On the other hand, the concentration of multivalent cations, such as Ca 2+ and Mg 2+ etc. in the molasses vinasse was 0.057 × 10 − 3 mol/L, which was determined using a chemical titration method (detailed in Section 2.5.3. Determination of multivalent cations). Therefore, present study inferred that multivalent cation, such as Ca 2+ and Mg 2+ etc. in the molasses vinasse were also exchanged onto strong acid cation resin, and retained on the resin, because that multivalent cation has stronger adsorption on the ion exchange resin than monovalent cation [21], and when the functional groups of the resin were desorbed using H2SO4 solution, multivalent cation, such as Ca 2+ and Mg 2+ etc. and sulfate anions in eluate could form crystal as the concentrations of CaSO4 and MgSO4 etc. reached the saturated level. These crystals would plug micro-porous of resin, increased the amount of eluent needed and decreased the utilization rate of H +.
Table 4 Elution rate of K+ using 0.3 and 0.4 mol/L H2SO4 solution stepwise desorption. Items
0.3 mol/L H2SO4 volume (mL)
0.4 mol/L H2SO4 volume (mL)
Total volume of H2SO4 eluent (mL)
Weight of H2SO4 (g)
K+ elution rate (%)
D1 D2 D3
600 400 200
1680 1820 1970
2280 2220 2170
85 85 85
99.7 99.8 99.7
Fig. 3. The profile of using both 0.3 and 0.4 mol/L H2SO4 stepwise elution potassium on the resin ZGC 108.
This also demonstrated the results that the operating H2SO4 concentration increased from 0.4 to 0.6 mol/L while the K + elution rate maintained about 99.6% w/w. 3.4. Changes of desorption routing In order to prevent crystals formation in the column, the H2SO4 concentration should be as low as possible, but the elution time and eluent quantity must be increased accordingly, which means higher resource and energy consumption for the recovery of potassium sulfate crystal. To alleviate this problem, stepwise elution routing shown as below should be used. The K + on the resin were stepwise eluted using the #D routing at an operating flow rate of 3BV/h and temperature at 35 °C, and the elution solution concentrations were 0.3 and 0.4 mol/L, respectively (Table 4 and Fig. 3). Table 4 has shown that the total quantity of H2SO4 used in three group experiments was the same (85 g), but the total volume was different with 2280, 2220 and 2170 mL, demonstrating higher elution rate of K+ on resin at 99.7, 99.8, and 99.7%, respectively. Fig. 3 showed that two-step eluting with different concentrations of H2SO4 broadened the width of elution curve at high level of K+ concentration. In consideration of the consumption volume of eluent needed, the K + should be eluted as follows. Firstly, the K + on the resin was eluted with 0.3 mol/L H2SO4 about 200 mL (D3 item in Table 3, account for 9.2% in total consumption volume). Secondly, the K + was eluted with 0.4 mol/L H2SO4. The elution rate of K + on resin was up to 99.7% and the total consumption volume of eluent was 4.3BV. In order to save more energy in extracting potassium sulfate crystal from the eluate and avoid preparing two concentrations of H2SO4 Table 5 Elution rate of K+ and utilization rate of H+ using 0.4 mol/L H2SO4 solution desorption in the #E routing. Items
Volume of first step (mL)
Volume of second step (mL)
Total volume of eluent (mL)
K+ elution rate (%)
H+ utilization rate (%)
Phenomena
E1
100
1510
1610
99.4
35.2
E2
200
1330
1530
99.6
38.1
E3
400
1280
1680
99.5
34.7
Some crystals in the #c column. No crystals in the #b and #c column. No crystals in the #b and #c column.
P.-J. Zhang et al. / Desalination 286 (2012) 210–216 Table 6 Extracting K2SO4 crystals from the eluate by concentration and cooling mother liquor. K+ Items Eluate H+ Condensate Mother liquor Crystallization volume(mL) rate of K+ (%) volume (g/1000 mL) (mol/L) water (mL) volume(mL) 1 2
1000 1000
13.5 13.5
0.57 0.57
939 956
52 28
76.2 89.3
solution, i.e. 0.3 and 0.4 mol/L H2SO4 solution. Devising the stepwise elution was the #E rooting (detailed in Section 2.3. Experimental routings and methods), and only 0.4 mol/L H2SO4 solution was flowed through the #E routing to elute the K + on exchange equilibrated resin with flow rate of 3BV/h at 35 °C. Table 5 showed that the #E2 group achieved the desired effect that crystals didn't appeared in columns and the elution rate of K + on resin was up to 99.6% w/w. On the other hand, the total consumption volume of eluent fell to 4.2BV, and the utilization rate of H + was 38.1%. In summary, the volume of 0.4 mol/L H2SO4 eluent using to the first step in the #E routing amount to 13% of total consumption volume shown promise as a new valuable way to reduce the eluent volume and get satisfied the elution rate of K + on resin. +
3.5. H in mother liquors (eluate after extraction of potassium sulfate) were recycled and reused The schematic diagram of extracted crystallized potassium sulfate from eluate was shown in Fig. 1b. The conditions for concentration were (1) vacuum −0.09 MPa, (2) speed 40 r/min, and (3) temperature 70 °C. 4 L eluate was firstly evaporated and concentrated, and then cooled in the reactor. The temperature was decreased with a ratio of 2 °C/h until lower than 20 °C. Little potassium sulfate crystallizing in mother liquor was prepared after filtrating with a membrane of 0.45 μm, and the mother liquor excess H+ was recycled as part of eluent in this experiment. The flow-process diagram was shown in Fig. 1c. Detailed data on crystallization and separation of potassium sulfate were shown in Table 6. It can be seen that the second group has a much higher crystallization rate of K + in eluate (89.3%) than the first group (76.2%) in about 1 L eluate. A suitable method for recycling H + in mother liquors was as follows. 1 L eluent was prepared with mother liquor of the second group, i.e. 28 mL mother liquor, by adding distilled water. The initial concentration of H + was 0.39 mol/L (H + recycled rate: about 49% w/w), and, then, H + concentration adjusted to 0.8 mol/L through adding H2SO4 solution. Further experiment with the #E routing (detailed in Section 2.3. Experimental routings and methods) was stated as follows, First, 220 mL eluent flowed through the columns, second, after the first step was carried out, transformed the valves to continue elute the K + on the resin with eluent at a flow rate of 3BV/h and temperature 35 °C. During elution process, 1 L eluent (prepared by mother liquor) was exhausted, then, the eluent was changed to 0.4 mol/L H2SO4 eluent (total volume was 700 mL). The elution rate of K + on resin was 99.6%. The test showed that re-using mother liquor might prevent formation crystal in the column, and after extracting potassium sulfate crystal from the eluant, H + in the mother liquor could be recycled. Therefore, the method proposed in the present study is effective and should be explored further as an application in treatment of distillery effluent. 4. Conclusion Strong acid–cation exchange resin (ZGC 108) could effectively remove potassium ions from molasses vinasse. Depending on the experimental data, the maximum breakthrough capability of wet resin was 56.79 mg K +/mL. Moreover, the volume of 0.4 mol/L H2SO4 eluent using to the first step in the #E routing amount to 13% of total consumption volume shown promise as a new valuable way to
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reduce the eluent volume (4.2BV) and get satisfied the elution rate of K + on resin (99.6%), and this routing could avoid sulfate crystallizing in the column. Finally, study of the recycling and reuse of H + in the mother liquor, after extracting K2SO4 crystals from the eluate, indicated that recycling about 49% H + in the eluate to elute the resin column was a potential means for industrial production of potassium salt. All in all, the ion exchange process using ZGC108 resin was potentially an effective means to remove potassium ions from the molasses vinasse because of its simplicity and lower raw material consumption. Acknowledgments All authors acknowledge the National Science Foundation of China (Grant No. 31071564), the Ministry of Science and Technology of China (fund No. 2011BAE16B04) and the Fundamental Research Funds for the Central Universities (2011ZM0105) for financial support. References [1] A.A. Khardenavis, A.N. Vaidya, M.S. Kumar, T. Chakrabarti, Utilization of molasses spentwash for production of bioplastics by waste activated sludge, Waste Manage. 29 (2009) 2558–2565. [2] N.K. Saha, M. Balakrishnan, V.S. Batra, Improving industrial water use: case study for an Indian distillery, Resour. Conserv. Recycl. 43 (2005) 163–174. [3] S. Mohana, B.K. Acharya, D. Madamwar, Distillery spent wash: Treatment technologies and potential applications, J. Hazard. Mater. 163 (2009) 12–25. [4] Y. Yavuz, EC and EF processes for the treatment of alcohol distillery wastewater, Sep. Purif. Technol. 53 (2007) 135–140. [5] Y. Satyawali, M. Balakrishnan, Wastewater treatment in molasses-based alcohol distilleries for COD and color removal: A review, J. Environ. Manage. 86 (2008) 481–497. [6] L.F. Ferreira, M. Aguiar, G. Pompeu, T.G. Messias, R.R. Monteiro, Selection of vinasse degrading microorganisms, World J. Microbiol. Biotechnol. 26 (2010) 1613–1621. [7] S. Yalcin, O. Eltan, M.A. Karsli, S. Yalcin, The nutritive value of modified dried vinasse (Pro Mass) and its effects on growth performance, carcass characteristics and some blood biochemical parameters in steers, Rev. Med. Vet. 161 (2010) 245–252. [8] N. Schultz, E. Lima, M.G. Pereira, E. Zonta, Residual Effects of Nitrogen, Potassium and Vinasse, Fertilization on Cane Plant and Ratoon Harvested with and without Straw Burning, Rev. Bras. Ciênc. Solo 34 (2010) 811–820. [9] S. Mahimairaja, N.S. Bolan, Problems and prospects of agricultural use of distillery spentwash in India, Third Australian and New Zealand Soil Science Societies Joint Conference, 2004, 5–9 December 2004. [10] R. Sowmeyan, G. Swaminathan, Effluent treatment process in molasses-based distillery industries: A review, J. Hazard. Mater. 152 (2008) 453–462. [11] K. Stemme, B. Gerdes, A. Harms, J. Kamphues, Beet-vinasse (condensed molasses solubles) as an ingredient in diets for cattle and pigs - nutritive value and limitations, J. Anim. Physiol. Anim. Nutr. 89 (2005) 179–183. [12] B. Fernandez, R. Bodas, O. Lopez-Campos, S. Andres, A.R. Mantecon, F.J. Giraldez, Vinasse added to dried sugar beet pulp: Preference rate, voluntary intake, and digestive utilization in sheep, J. Anim. Sci. 87 (2009) 2055–2063. [13] M. Decloux, A. Bories, R. Lewandowski, C. Fargues, A. Mersad, M.L. Lameloise, et al., Interest of electrodialysis to reduce potassium level in vinasses. Preliminary experiments, Desalination 146 (2002) 393–398. [14] Y. Satyawali, M. Balakrishnan, Treatment of distillery effluent in a membrane bioreactor (MBR) equipped with mesh filter, Sep. Purif. Technol. 63 (2008) 278–286. [15] L.A. Richards, B.S. Richards, A.I. Schaefer, Renewable energy powered membrane technology: Salt and inorganic contaminant removal by nanofiltration/reverse osmosis, J. Membr. Sci. 369 (2011) 188–195. [16] M. Acevedo-Morantes, G. Colon, A. Realpe, Electrolytic removal of nitrate and potassium from wheat leachate using a four compartment electrolytic cell, Desalination 278 (2011) 354–364. [17] K. Xu, C. Wang, H. Liu, Y. Qian, Simultaneous removal of phosphorus and potassium from synthetic urine through the precipitation of magnesium potassium phosphate hexahydrate, Chemosphere 84 (2011) 207–212. [18] M.Y.A. Mollah, R. Schennach, J.R. Parga, D.L. Cocke, Electrocoagulation (EC) science and applications, J. Hazard. Mater. 84 (2001) 29–41. [19] J.D. Rincon, N.M. Cabrales, F.M. Martinez, Total Solid Removal of Vinasse by Electrocoagulation-Electroflotation, Dyna-Colombia 76 (2009) 41–47. [20] G.S. Chubnovskii, Flame photometer for quantitative determination of sodium and potassium, Vopr. Med. Khim. 5 (1959) 458–465. [21] S.M. Zhu, S.J. Yu, X. Fu, X.S. Chai, L.A. Zhu, X.X. Yang, A modified quentin method for desalting thin juice and mother liquor B in beet sugar industry, Desalination 268 (2010) 214–220. [22] T.E. Kose, N. Ozturk, Boron removal from aqueous solutions by ion-exchange resin: Column sorption-elution studies, J. Hazard. Mater. 152 (2008) 744–749.
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[23] A. Elmidaoui, F. Lutin, L. Chay, M. Taky, M. Tahaikt, M.R.A. Hafidi, Removal of melassigenic ions for beet sugar syrups by electrodialysis using a new anionexchange membrane, Desalination 148 (2002) 143–148. [24] Z. Aksu, F. Gonen, Biosorption of phenol by immobilized activated sludge in a continuous packed bed: prediction of breakthrough curves, Process. Biochem. 39 (2004) 599–613. [25] F. Helfferich, Ion Exchange, McGraw-Hill Book Company, Inc, New York, 1962, pp. 95–308.
[26] B.R. Staples, Activity and Osmotic Coefficients of Aqueous Sulfuric-Acid at 298.15-K, J. Phys. Chem. Ref. Data 10 (1981) 779–798. [27] H.A. Michelsen, A parameterization for the activity of H+ in aqueous sulfuric acid solutions, Geophys. Res. Lett. 25 (1998) 3571–3573. [28] A.F. Vorob'ev, D.I. Mustafin, S.V. Senatorova, Potassium sulfate solubility in aqueous acetonitrile, Russ. J. Inorg. Chem. 48 (2003) 1434–1435.
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Using strong acid–cation exchange resin to reduce potassium level in molasses vinasses Ping-Jun Zhang, Zhen-Gang Zhao, Shu-Juan Yu ⁎, Yong-Guang Guan, Dan Li, Xiang He College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, China Guangdong Province Key Laboratory for Green Processing of Natural Products and Product Safety, South China University of Technology, Guangzhou 510640, China
a r t i c l e
i n f o
Article history: Received 12 July 2011 Received in revised form 25 October 2011 Accepted 9 November 2011 Available online 15 December 2011 Keywords: Molasses vinasse Desalting Potassium Ion-exchange
a b s t r a c t Molasses-based distilleries are one of the most vulnerable to pollution industries, which always generate large volumes of high strength vinasse. Recently, one of the most effective re-applications/reuse of vinasse is concentrating the molasses vinasse to prepare as fodder additive for animal food. However, the dosage of molasses vinasse to be added as animal feed is always limited because of the unexpectedly high potassium content in molasses vinasse. In present study, potassium ions were firstly extracted from molasses vinasses using a strong acid–cation exchange resin, and then desorbed from the resin and dissolved into the eluate by H2SO4 solution as the strong acid–cation exchange resin was regenerated. Finally, evaluation to recycle and reuse the mother liquor (once-used eluant), after extracting K2SO4 crystals from the eluant, was investigated. Results indicated that using the mother liquor to elute the resin column which absorbing K+ from molasses vinasse was a potential means for industrial production of potassium salt. Meanwhile, the molasses vinasse which has removed most potassium ions might be used as animal feed. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Molasses vinasse is the remain of the fermentation and distillation of alcohol from cane and beet molasses [1]. On an average 8–15 L of effluent is generated for every liter of alcohol produced [2]. On the other hand, the molasses vinasse is extensively growing due to widespread industrial applications of alcohol such as in pharmaceuticals, food, perfumery, fuel, etc. [3]. The effluent always has a high level of organic content such as crude proteins, lactic acid, glycerol, cholesterol, amino acid and reducing sugars (COD in the range of 80,000–100,000 mg/L and BOD in the range of 40,000–50,000 mg/L), strong odor and dark brown color [4–7], and it also contains nutrients in the form of nitrogen (1660–4200 mg/L), phosphorus (225– 3038 mg/L) and potassium (9600–17,475 mg/L) [8–10], which have resulted in serious environmental problems, such as eutrophication of bays, lakes, and inland seas. However, in addition to pollution, increasingly stringent environmental regulations are forcing distilleries to improve existing treatment and also explore alternative methods of effluent management [5]. Recently, many research teams focused on the study of preparing nutriment fodder using molasses vinasses. However, the dosage of molasses vinasses was also limited, because unexpectedly high potassium content in molasses vinasse could lead to bulls and pigs diarrhea [7,11–13]. The removal of potassium from molasses vinasse has been ⁎ Corresponding author at: #381, Wushan road, Guangzhou, China. Tel./fax: + 86 20 87113668. E-mail address: [email protected] (S.-J. Yu). 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.11.024
widely investigated, and various techniques proposed for its removal, such as chemical precipitation, electrodialysis, reverse osmosis and ion exchange. Of these processes, chemical precipitation, electrodialysis and reverse osmosis have been widely used for the treatment of potassium in molasses vinasse [4,13–19]; however, these techniques are expensive, and require complex and strict control of the operating conditions. Conversely, ion exchange technique is easy to operate and allows the potassium to be recycled. The successful accomplishment of this technique depends on the choice of an adequate eluant and routing. The study aims to fully reduce potassium level in molasses vinasses by using strong acid–cation exchange resin (ZGC 108). Firstly, we chose acids which were representative of groups commonly found in market. Potassium ions were then extracted from molasses vinasses using a strong acid–cation exchange resin, and desorbed from the resin and dissolved into the eluate during the resin regeneration process using chosen acid solution. Finally, the reused of mother liquor (as part of the eluant for the next cycle), which is the eluate after extracting of potassium salt by crystallization, to more fully utilize the remaining H + was investigated. 2. Materials and methods 2.1. Experimental materials and main apparatus ZGC108 ion exchange resin (Na + form) (Hangzhou Zheng Guang Co., Ltd, China) was used to extract K + from sugarcane molasses vinasse (Zhongneng Ethanol Co., Ltd, China). All the chemicals used
P.-J. Zhang et al. / Desalination 286 (2012) 210–216
were analytical pure and purchased from Guangzhou Chemical Co., Ltd. (Guangzhou, China). In this experiment, main equipments and their application were shown as follows. A flame photometer (FP640, Aimusheng of Shanghai Co., Ltd, China) was used for potassium analysis [20,21]. A constant flow pump (HL-200B, Jingke Shiye of Shanghai Co., Ltd, China) was used to provide a stable flow velocity of leacheate. A thermostatic water bath (Pudong Rongfeng of Shanghai Co., Ltd, China) was provided for the stabilization of temperature. A reactor (total volume, 1 L) (Asahi Seisakusho Inc, Japan) with a stirrer (IKA, Internet Khazak Alippe GmbH & Co, Germany) and a programmable cooling & heating controller (CC2, Huber Kältemaschinenbau GmbH, Germany) was used to produce potassium sulfate crystals. A conductivity meter (DDS-11A, Leici Xinjing of Shanghai Co., Ltd, China) was used for the conductivity measurement of distilled water. The ion exchange columns were made to our specifications by a glass apparatus company (Guangzhou Tianhe Precision Instruments Wholesale Division of the Department of Glass Co. LTD). 2.2. Selection of eluents Four considered acids were evaluated for elution capacity of K + on the resin. First, four 50 mL of the wet resin in the K + form were added to 4 flasks containing 250 ml of a labeled 0.3 mol/L H2SO4, 0.6 mol/L HCl, 0.2 mol/L H3PO4 and 0.6 mol/L CH3COOH, respectively, water solution. The flasks were maintained at a temperature of 35 °C and agitated (50 rpm) in a thermostatic water bath. Hourly samples (5 ml) were taken for K + analysis until the concentration was unchanged. The desorption capacity of K + was calculated per wet volume of resin according to the determined data. 2.3. Experimental routings and methods A schematic drawing of ion-exchange experimental facilities was shown in Fig. 1a. It was performed in three glass columns, #a (2.6 cm internal diameter and 10 cm length), #b and #c (3.3 cm internal diameter and 30 cm length). Firstly, the #a column was packed with 50 mL quartz sand with particle size distribution of 0.05– 0.20 mm, then, washed using distilled water until the conductivity of the effluent was lower than 2μS/cm. At last, both #b and #c columns were filled with 180 mL wet-settled bed volume (BV) of resin, respectively. The column adsorption experiments were carried out by three routing (#A, #B and #C routing). In the #A routing, the 3, 5, 6, 8, 10, 11 valves were closed while the 1, 2, 4, 7, 9, 12 valves were opened. The #a, #b and #c columns were connected in series, respectively. Molasses vinasse was down flowed from #a to #b, and then to #c columns. In the #B routing, the 3, 4, 7, 8, 9, 12 valves were closed while the 1, 2, 5, 6, 10, 11 valves were opened. The #a, #b and #c columns were connected in series, respectively. Molasses vinasse which was down flowed from #a, was up flowed past #b and then past #c columns. In the #C routing, two steps were carried out. First, the 3, 6, 7, 10, 11 valves were closed while the 1, 2, 4, 5, 8, 9, 12 valves were opened. The #b and #c were concurrent flow, both #b and #c were connected with the exit of #a. 1620 mL, i.e. 4.5BV, molasses vinasse which was down flowed from #a column, was then down flowed equally past #b and #c columns. Second, after the first step was carried out, the 3, 5, 6, 8, 10, 11 valves were closed while the 1, 2, 4, 7, 9, 12 valves were opened. The #a, #b and #c columns were connected in series. Molasses vinasse was down flowed past #a, #b, and #c columns in tandem. The molasses vinasse was flowed past the columns at a flow rate of 360 mL/h (1BV/h) using a constant flow pump. Each successive 100 mL fractions of the effluent were collected using a fraction
211
collector. Breakthrough curves were obtained by analyzing each fraction using a flame photometer. The column elution experiments were carried out using two routing (#D and #E routing). In the #D routing, the 1, 2, 5, 6, 8, 10, 11 valves were closed and the 3, 4, 7, 9, 12 valves were opened. The #b and #c columns were connected in series. Sulfuric acid solution with different concentrations, 0.2 to 0.6 mol/L, was down flowed past #b and #c columns in tandem. In the #E routing, two steps were carried out. First, the 1, 2, 6, 7, 10, 11 valves were closed while the 3, 4, 5, 8, 9, 12 valves were opened. The #b and #c were concurrent flow. Sulfuric acid solution was down flowed equally past #b and #c columns at a flow rate of 1080 mL/h, i.e. 3BV/h, at 35 °C. Second, after the first step was carried out, the 1, 2, 5, 6, 8, 10, 11 valves were closed and the 3, 4, 7, 9, 12 valves were opened. The #b and #c columns were connected in series. Sulfuric acid solution was down flowed past #b and #c columns in tandem at a flow rate of 1080 mL/h, i.e. 3BV/h, at 35 °C. The different concentration of sulfuric acid solutions were used for column elution as the flow rate of 3BV/h (1080 mL/h) at 35 °C. The elution was completed as the concentration of potassium ions in the elution solution was lower than 0.01 g/L.
2.4. Resin pretreatment The ion-exchange resin that was pretreated as follows. The resin ZGC108 was soaked with distilled water in round glass container for 24 h, and then, treated with 1 mol/L NaOH solution (triple resin volume) and then 1 mol/L HCl solution (triple resin volume) for 6 h, respectively. Finally, the resin was washed with distilled water until the pH of the wash water was about 6.5. After the pretreatment in this experiment, the functional sites on resin were changed from Na + form to H + form [22].
2.5. Chemical analysis 2.5.1. Determination of K + K + in the sample was determined by flame photometer [21,23]. Sample was diluted some fold for the K + determination. Standard solutions of two different concentrations were used for calibration: 20 μg K +/mL and 80 μg K +/mL.
2.5.2. Determination of H + The concentration of H + in the solution was determined using a chemical titration method. A 10.0 mL sample of solution was shaken with 30.0 mL of distilled water and 1 mL of phenolphthalein solution (0.5 g/L). Then the mixture was titrated with a 0.100 mol/L NaOH solution from colourless to just red colorimetric endpoint with the volume of titrant used recorded as V mL. The concentration of H + in the solution was calculated as 0.100× V/10.0, in mol/L.
2.5.3. Determination of multivalent cations The concentration of multivalent cations, such as Ca 2+ and Mg 2+ etc. in the molasses vinasse was determined using a chemical titration method. A 5 mL sample of molasses vinasse was shaken with 95 ml of distilled water, 5–15 mL of ammonia buffer (pH 10.0–13.0) and 0.1 g of eriochrome black T (EBT) which is a complexometric indicator that is part of the complexometric titrations. Then the mixture was titrated with a 3.57 mmol/L EDTA–Na2 solution from purple to blue colorimetric endpoint, with the volume of titrant used recorded as V, in mL. The concentration of multivalent cations in the molasses vinasse was calculated as 3.57 × V/5.0, in mmol/L.
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Fig. 1. Schematic drawing of experimental setup and process: (a) Fixed-bed ion exchange column system; (b) K2SO4 crystallization experimental setup; and (c) Recovery process.
2.6. Computing methods Sorption capacity of the resin (q; mg/mL) was calculated based on Eq. (1) [22,24]. Vt
q ¼ ∫0
C 0 −CÞdV V′
ð1Þ
where, V’ (mL), Co (mg/mL), C (mg/mL) and Vt (mL) were the volume of the ion-exchange resin, the initial potassium concentration,
the effluent potassium concentration and the effluent volume(V) as a function of time (t), respectively. The K + in the resin elution rate (Q; %, w/w) was calculated based on Eq. (2). Q¼
ab 100% c
ð2Þ
where, a (mg/mL), b (mL) and c (mg) means the potassium concentration in the eluent, the total eluent volume and the sorption capacity of the resin in the columns, respectively.
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The H + in the H2SO4 eluate utilization rate (N; %, w/w) was calculated based on Eq. (3). N¼
de 100% f g
Table 2 Adsorption capacity of the resin (ZGC 108) for K+ at three routings. Item
Breakthrough volume (mL)
Breakthrough capacity (mg/mL)
Saturated volume (mL)
Saturated capacity (mg/mL)
#A #B #C
2000 1910 2065
54.07 52.84 56.79
2410 2460 2330
65.81 65.96 66.58
ð3Þ
where, d (mol/L), e (L), f (mol/L) and g (L) means the H + concentration in the total eluant, the total eluant volume, the H + concentration in the total eluent and the total eluent volume, respectively. 3. Results and discussion 3.1. Choice of the acid Compared on the basis of acids performance in desorption K + from the resin, the acids (H2SO4, HCl, H3PO4 and CH3COOH, respectively) treatment of the resin was introduced. Table 1 shows that the acids are evident demonstrating highest K + desorption capacity H2SO4 and HCl at 45.5 and 47.0 mg K +/ml wet resin, respectively. Of these two, the HCl acid has a little higher desorption quantity than H2SO4 acid. In general, acid in a strong acid form can desorb more K + from strong acid–cation exchange resin (ZGC108) than those acids in a mediate strong acid (H3PO4) or weak acid(CH3COOH) at 18.5 and 8.2 mg K +/ml wet resin, respectively, which may be explained by law of mass action [25]. Under the testing conditions, the H ions in strong acid are easier di ociation than that in mediate strong or weak acid. Therefore, on the same conditions, acid (H2SO4 and HCl) in strong acid form is more suitable to desorb K + on the resin than in mediate strong (H3PO4) or weak (CH3COOH) acid form. In practice, acid HCl is a volatile acid, and it is not suitable to be reused. Based on these considerations, acid H2SO4 was selected as the acid with which to continue the study of eluting K + on the resin.
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among three routings, the least breakthrough exchange capacity value was the #B routing (see Table 2), which may be explained by back diffusion. Under the #B routing testing conditions, the back diffusion velocity of the K + in upflow molasses vinasse was faster than K + in downflow molasses vinasse, Therefore, the #B routing wasn't suitable to desalting the K + in the molasses vinasse, and the back diffusion between the molasses vinasse containing K + and the molasses vinasse without K + played a significant role on the column performance. However, using the #C routing that might avoid the drawback of the #A and #B routing and got satisfied breakthrough exchange capacity, and, in general, 6–7 h of adsorption time was suitable for an ion exchange operation unit for economic reasons. Then, at the same condition, experiments using the #C routing were carried out in triplicates. Means and standard deviations of the data were calculated for each treatment. Analysis of variance (ANOVA) was carried out to determine any significant differences among the applied treatments by the SPSS package (SPSS 10.0 for windows), and the equilibrium saturated exchange capacity was constant, about 56.78 mg K +/ mL wet resin(P b 0.05). Based on these considerations, the #C routing was selected as the adsorption routing with which to continue the study of elution condition.
3.3. Changes of H2SO4 concentration 3.2. Changes of exchange routing
1.0 A B C
0.8
0.6
C/C0
In order to select the most suitable routing for desalting, three routings (#A, #B and #C, respectively) which detailed in Section 2.3 (Experimental routings and methods) were recommended to adsorb K + from sugarcane molasses vinasse and the different routings schematic diagram was shown in Fig. 1a. The condition for carrying out ion exchange was (1) concentration 9.9 mg K +/mL, (2) pH of influent 4.0, (3) temperature 28 °C, (4) flow rate 1BV/h (360 mL/hr). In Table 2, the #A, #B, and #C routing indicated higher K + saturated exchange capacity at 65.81, 65.96 and 66.58 mg K +/mL wet resin, respectively. And the profiles of breakthrough curves were shown in Fig. 2 that demonstrated the breakthrough exchange ability of the ZGC108 resin, based on the ratios of the areas under curves from C/ Co = 0 to C/Co = 1. The #C routing got a higher breakthrough exchange capacity (56.79 mg K +/mL wet resin) than #A or #B routing (54.07 and 52.84 mg K +/mL wet resin, respectively). Some discussions were detailed as follows. Firstly, the K + in the molasses vinasse was exchanged completely by activation of functional sites on the #b column resin in the beginning stage, then, the pores of resin in the #c column was clogged by some bigger molecules in sugarcane molasses vinasse, resulting in lower breakthrough exchange capacity values of the resin, which was detected as the #A routing was on. Moreover,
The aim of this test was to elute the K + on the functional sites of the resin with H2SO4 solution. The advantage was that the extraction of K + and regeneration of resin took place simultaneously, because the functional group of the resin was changed from K + to H + form in a single desorption process using H2SO4 solution as eluent. The K + in five groups exchange equilibrated resin were adsorbed using the #C routing, then the K + on the resin were eluted using the #D routing (detailed in Section 2.3. Experimental routings and methods) by 6 BV H2SO4 solution at a flow rate of 3BV/h with 35 °C, and the concentrations of H2SO4 eluant solution were 0.6, 0.5, 0.4, 0.3 and 0.2 mol/L, respectively.
0.4
0.2 Table 1 Desorption capacity of K+ on the resin using different acids.
0.0 Acids
Concentration (mol/L)
Specific desorption capacity (mg K+/ml wet resin)
H2SO4 HCl H3PO4 CH3COOH
0.3 0.6 0.2 0.6
45.5 47.0 18.5 8.2
1400
1600
1800
2000
2200
2400
2600
2800
V/mL Fig. 2. Breakthrough curves for the removal of potassium by the resin ZGC 108 at three routings.
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30
Table 3 The K+ elution rate and H+ utilization rate as a function of H2SO4 concentrations. Elution volume (BV)
K+ elution H+ rate (%) utilization rate (%)
Phenomena
0.6
6
99.6
22.3
0.5
6
99.7
26.7
0.4
6
99.6
32.8
0.3
6
93.4
42.1
0.2
6
86.8
59.3
Many crystals in the middle of #b column, several in #c column. Some crystals on the bottom of #b column, many on the top and middle part of #c column. No crystals in the #b column, but several in the middle and lower part of #c column. No crystals in the #b and #c column. No crystals in the #b and #c column.
K+ conceration (g/L)
25
H2SO4 concentration (mol/L)
D1 D2 D3
20 15 10 5 0 0
1
2
3
4
5
6
7
Eluate volume (mL/mL resin) Table 3 shows the effects of different H2SO4 concentration eluant on desorption of the K + on the resin by batch treatment. As shown in Table 3, about 99.6% of the K + on the resin was desorbed when the operating H2SO4 concentration from 0.4 to 0.6 mol/L. The K + elution rate was increased from 86.8 to 99.6% when the H2SO4 concentration ranged from 0.2 to 0.4 mol/L. The reason for the lower desorption rate in the H2SO4 concentration at 0.2 and 0.3 mol/L may be related to the activity coefficient of H ions in the eluent [25]. According to the data in Table 3 inferred that the activity coefficient of H ions in water solutions increased along with the increase in the H2SO4 concentration between 0.2 and 0.4 mol/L, while the activity coefficient of H ions didn't changed between 0.4 and 0.6 mol/L. A similar finding was detailed by Staples et al., (1981) and Michelsen et al., (1998), who indirectly confirmed that the activity coefficient of H ions in water solution was connected with H2SO4 concentration [26,27]. As expected, the H + utilization rate decreased from 59.3 to 22.3% w/w with the concentration of H2SO4 changed from 0.2 to 0.6 mol/L (see Table 3). On the other hand, an interesting phenomenon that some crystals appeared in the columns (#b and #c columns) was observed with the H2SO4 concentration between 0.5 and 0.6 mol/L (see Table 3). The maximum level of K + in eluate was 0.705 mol/L (27.5 g K +/L) at 35 °C, and, according to the literature [28], the solubility of K2SO4 was about 0.706 mol/L at the same temperature. It could be inferred that there was no K2SO4 crystal in eluate in this condition. On the other hand, the concentration of multivalent cations, such as Ca 2+ and Mg 2+ etc. in the molasses vinasse was 0.057 × 10 − 3 mol/L, which was determined using a chemical titration method (detailed in Section 2.5.3. Determination of multivalent cations). Therefore, present study inferred that multivalent cation, such as Ca 2+ and Mg 2+ etc. in the molasses vinasse were also exchanged onto strong acid cation resin, and retained on the resin, because that multivalent cation has stronger adsorption on the ion exchange resin than monovalent cation [21], and when the functional groups of the resin were desorbed using H2SO4 solution, multivalent cation, such as Ca 2+ and Mg 2+ etc. and sulfate anions in eluate could form crystal as the concentrations of CaSO4 and MgSO4 etc. reached the saturated level. These crystals would plug micro-porous of resin, increased the amount of eluent needed and decreased the utilization rate of H +.
Table 4 Elution rate of K+ using 0.3 and 0.4 mol/L H2SO4 solution stepwise desorption. Items
0.3 mol/L H2SO4 volume (mL)
0.4 mol/L H2SO4 volume (mL)
Total volume of H2SO4 eluent (mL)
Weight of H2SO4 (g)
K+ elution rate (%)
D1 D2 D3
600 400 200
1680 1820 1970
2280 2220 2170
85 85 85
99.7 99.8 99.7
Fig. 3. The profile of using both 0.3 and 0.4 mol/L H2SO4 stepwise elution potassium on the resin ZGC 108.
This also demonstrated the results that the operating H2SO4 concentration increased from 0.4 to 0.6 mol/L while the K + elution rate maintained about 99.6% w/w. 3.4. Changes of desorption routing In order to prevent crystals formation in the column, the H2SO4 concentration should be as low as possible, but the elution time and eluent quantity must be increased accordingly, which means higher resource and energy consumption for the recovery of potassium sulfate crystal. To alleviate this problem, stepwise elution routing shown as below should be used. The K + on the resin were stepwise eluted using the #D routing at an operating flow rate of 3BV/h and temperature at 35 °C, and the elution solution concentrations were 0.3 and 0.4 mol/L, respectively (Table 4 and Fig. 3). Table 4 has shown that the total quantity of H2SO4 used in three group experiments was the same (85 g), but the total volume was different with 2280, 2220 and 2170 mL, demonstrating higher elution rate of K+ on resin at 99.7, 99.8, and 99.7%, respectively. Fig. 3 showed that two-step eluting with different concentrations of H2SO4 broadened the width of elution curve at high level of K+ concentration. In consideration of the consumption volume of eluent needed, the K + should be eluted as follows. Firstly, the K + on the resin was eluted with 0.3 mol/L H2SO4 about 200 mL (D3 item in Table 3, account for 9.2% in total consumption volume). Secondly, the K + was eluted with 0.4 mol/L H2SO4. The elution rate of K + on resin was up to 99.7% and the total consumption volume of eluent was 4.3BV. In order to save more energy in extracting potassium sulfate crystal from the eluate and avoid preparing two concentrations of H2SO4 Table 5 Elution rate of K+ and utilization rate of H+ using 0.4 mol/L H2SO4 solution desorption in the #E routing. Items
Volume of first step (mL)
Volume of second step (mL)
Total volume of eluent (mL)
K+ elution rate (%)
H+ utilization rate (%)
Phenomena
E1
100
1510
1610
99.4
35.2
E2
200
1330
1530
99.6
38.1
E3
400
1280
1680
99.5
34.7
Some crystals in the #c column. No crystals in the #b and #c column. No crystals in the #b and #c column.
P.-J. Zhang et al. / Desalination 286 (2012) 210–216 Table 6 Extracting K2SO4 crystals from the eluate by concentration and cooling mother liquor. K+ Items Eluate H+ Condensate Mother liquor Crystallization volume(mL) rate of K+ (%) volume (g/1000 mL) (mol/L) water (mL) volume(mL) 1 2
1000 1000
13.5 13.5
0.57 0.57
939 956
52 28
76.2 89.3
solution, i.e. 0.3 and 0.4 mol/L H2SO4 solution. Devising the stepwise elution was the #E rooting (detailed in Section 2.3. Experimental routings and methods), and only 0.4 mol/L H2SO4 solution was flowed through the #E routing to elute the K + on exchange equilibrated resin with flow rate of 3BV/h at 35 °C. Table 5 showed that the #E2 group achieved the desired effect that crystals didn't appeared in columns and the elution rate of K + on resin was up to 99.6% w/w. On the other hand, the total consumption volume of eluent fell to 4.2BV, and the utilization rate of H + was 38.1%. In summary, the volume of 0.4 mol/L H2SO4 eluent using to the first step in the #E routing amount to 13% of total consumption volume shown promise as a new valuable way to reduce the eluent volume and get satisfied the elution rate of K + on resin. +
3.5. H in mother liquors (eluate after extraction of potassium sulfate) were recycled and reused The schematic diagram of extracted crystallized potassium sulfate from eluate was shown in Fig. 1b. The conditions for concentration were (1) vacuum −0.09 MPa, (2) speed 40 r/min, and (3) temperature 70 °C. 4 L eluate was firstly evaporated and concentrated, and then cooled in the reactor. The temperature was decreased with a ratio of 2 °C/h until lower than 20 °C. Little potassium sulfate crystallizing in mother liquor was prepared after filtrating with a membrane of 0.45 μm, and the mother liquor excess H+ was recycled as part of eluent in this experiment. The flow-process diagram was shown in Fig. 1c. Detailed data on crystallization and separation of potassium sulfate were shown in Table 6. It can be seen that the second group has a much higher crystallization rate of K + in eluate (89.3%) than the first group (76.2%) in about 1 L eluate. A suitable method for recycling H + in mother liquors was as follows. 1 L eluent was prepared with mother liquor of the second group, i.e. 28 mL mother liquor, by adding distilled water. The initial concentration of H + was 0.39 mol/L (H + recycled rate: about 49% w/w), and, then, H + concentration adjusted to 0.8 mol/L through adding H2SO4 solution. Further experiment with the #E routing (detailed in Section 2.3. Experimental routings and methods) was stated as follows, First, 220 mL eluent flowed through the columns, second, after the first step was carried out, transformed the valves to continue elute the K + on the resin with eluent at a flow rate of 3BV/h and temperature 35 °C. During elution process, 1 L eluent (prepared by mother liquor) was exhausted, then, the eluent was changed to 0.4 mol/L H2SO4 eluent (total volume was 700 mL). The elution rate of K + on resin was 99.6%. The test showed that re-using mother liquor might prevent formation crystal in the column, and after extracting potassium sulfate crystal from the eluant, H + in the mother liquor could be recycled. Therefore, the method proposed in the present study is effective and should be explored further as an application in treatment of distillery effluent. 4. Conclusion Strong acid–cation exchange resin (ZGC 108) could effectively remove potassium ions from molasses vinasse. Depending on the experimental data, the maximum breakthrough capability of wet resin was 56.79 mg K +/mL. Moreover, the volume of 0.4 mol/L H2SO4 eluent using to the first step in the #E routing amount to 13% of total consumption volume shown promise as a new valuable way to
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reduce the eluent volume (4.2BV) and get satisfied the elution rate of K + on resin (99.6%), and this routing could avoid sulfate crystallizing in the column. Finally, study of the recycling and reuse of H + in the mother liquor, after extracting K2SO4 crystals from the eluate, indicated that recycling about 49% H + in the eluate to elute the resin column was a potential means for industrial production of potassium salt. All in all, the ion exchange process using ZGC108 resin was potentially an effective means to remove potassium ions from the molasses vinasse because of its simplicity and lower raw material consumption. Acknowledgments All authors acknowledge the National Science Foundation of China (Grant No. 31071564), the Ministry of Science and Technology of China (fund No. 2011BAE16B04) and the Fundamental Research Funds for the Central Universities (2011ZM0105) for financial support. References [1] A.A. Khardenavis, A.N. Vaidya, M.S. Kumar, T. Chakrabarti, Utilization of molasses spentwash for production of bioplastics by waste activated sludge, Waste Manage. 29 (2009) 2558–2565. [2] N.K. Saha, M. Balakrishnan, V.S. Batra, Improving industrial water use: case study for an Indian distillery, Resour. Conserv. Recycl. 43 (2005) 163–174. [3] S. Mohana, B.K. Acharya, D. Madamwar, Distillery spent wash: Treatment technologies and potential applications, J. Hazard. Mater. 163 (2009) 12–25. [4] Y. Yavuz, EC and EF processes for the treatment of alcohol distillery wastewater, Sep. Purif. Technol. 53 (2007) 135–140. [5] Y. Satyawali, M. Balakrishnan, Wastewater treatment in molasses-based alcohol distilleries for COD and color removal: A review, J. Environ. Manage. 86 (2008) 481–497. [6] L.F. Ferreira, M. Aguiar, G. Pompeu, T.G. Messias, R.R. Monteiro, Selection of vinasse degrading microorganisms, World J. Microbiol. Biotechnol. 26 (2010) 1613–1621. [7] S. Yalcin, O. Eltan, M.A. Karsli, S. Yalcin, The nutritive value of modified dried vinasse (Pro Mass) and its effects on growth performance, carcass characteristics and some blood biochemical parameters in steers, Rev. Med. Vet. 161 (2010) 245–252. [8] N. Schultz, E. Lima, M.G. Pereira, E. Zonta, Residual Effects of Nitrogen, Potassium and Vinasse, Fertilization on Cane Plant and Ratoon Harvested with and without Straw Burning, Rev. Bras. Ciênc. Solo 34 (2010) 811–820. [9] S. Mahimairaja, N.S. Bolan, Problems and prospects of agricultural use of distillery spentwash in India, Third Australian and New Zealand Soil Science Societies Joint Conference, 2004, 5–9 December 2004. [10] R. Sowmeyan, G. Swaminathan, Effluent treatment process in molasses-based distillery industries: A review, J. Hazard. Mater. 152 (2008) 453–462. [11] K. Stemme, B. Gerdes, A. Harms, J. Kamphues, Beet-vinasse (condensed molasses solubles) as an ingredient in diets for cattle and pigs - nutritive value and limitations, J. Anim. Physiol. Anim. Nutr. 89 (2005) 179–183. [12] B. Fernandez, R. Bodas, O. Lopez-Campos, S. Andres, A.R. Mantecon, F.J. Giraldez, Vinasse added to dried sugar beet pulp: Preference rate, voluntary intake, and digestive utilization in sheep, J. Anim. Sci. 87 (2009) 2055–2063. [13] M. Decloux, A. Bories, R. Lewandowski, C. Fargues, A. Mersad, M.L. Lameloise, et al., Interest of electrodialysis to reduce potassium level in vinasses. Preliminary experiments, Desalination 146 (2002) 393–398. [14] Y. Satyawali, M. Balakrishnan, Treatment of distillery effluent in a membrane bioreactor (MBR) equipped with mesh filter, Sep. Purif. Technol. 63 (2008) 278–286. [15] L.A. Richards, B.S. Richards, A.I. Schaefer, Renewable energy powered membrane technology: Salt and inorganic contaminant removal by nanofiltration/reverse osmosis, J. Membr. Sci. 369 (2011) 188–195. [16] M. Acevedo-Morantes, G. Colon, A. Realpe, Electrolytic removal of nitrate and potassium from wheat leachate using a four compartment electrolytic cell, Desalination 278 (2011) 354–364. [17] K. Xu, C. Wang, H. Liu, Y. Qian, Simultaneous removal of phosphorus and potassium from synthetic urine through the precipitation of magnesium potassium phosphate hexahydrate, Chemosphere 84 (2011) 207–212. [18] M.Y.A. Mollah, R. Schennach, J.R. Parga, D.L. Cocke, Electrocoagulation (EC) science and applications, J. Hazard. Mater. 84 (2001) 29–41. [19] J.D. Rincon, N.M. Cabrales, F.M. Martinez, Total Solid Removal of Vinasse by Electrocoagulation-Electroflotation, Dyna-Colombia 76 (2009) 41–47. [20] G.S. Chubnovskii, Flame photometer for quantitative determination of sodium and potassium, Vopr. Med. Khim. 5 (1959) 458–465. [21] S.M. Zhu, S.J. Yu, X. Fu, X.S. Chai, L.A. Zhu, X.X. Yang, A modified quentin method for desalting thin juice and mother liquor B in beet sugar industry, Desalination 268 (2010) 214–220. [22] T.E. Kose, N. Ozturk, Boron removal from aqueous solutions by ion-exchange resin: Column sorption-elution studies, J. Hazard. Mater. 152 (2008) 744–749.
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