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CaCO3 production using liquid waste from Solvay method
Journal of Cleaner Production 19 (2011) 751e756
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
CaCO3 production using liquid waste from Solvay method Mieczys1aw Trypu c*, Katarzyna Bia1owicz , Poland Nicolaus Copernicus University, Faculty of Chemistry, Department of Chemical Technology, Gagarina 7, 87-100 Torun
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 March 2010 Received in revised form 9 November 2010 Accepted 12 November 2010 Available online 8 December 2010
Process of obtaining CaCO3 from the waste post-distillation liquid DS and post-filtration liquid from Solvay method of the soda production at 303 K was investigated. Reagents were dosed in a stoichiometric ratio without dilution, for different concentrations of the DS and post-filtration liquids. The dosage time was varied in the range 2e30 min, the reagent stirring rate was 500 rpm. For the obtained samples of CaCO3, the bulk and packing densities, water, paraffin oil and dibutyl phthalate absorption capacities, distribution of the particle size as well as the crystalline form were determined. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Solvay method Calcium carbonate Post-distillation liquor (DS) Post-filtration liquid Bulk density Packing density
1. Introduction In the EU countries, the calcinated soda is produced exclusively with the Solvay method, due to the general availability and relatively low prices of the substrates used. Besides numerous advantages, the Solvay method has many disadvantages. It is characterized by low material and energy efficiency and high noxiousness for the natural environment. The energy costs constitute 33% of the overall costs, while the degree of utilization of limestone and coke is 69 and 53%, respectively. The basic step of that method is carbonization of the ammoniated brine, for which the average efficiency calculated relatively to the sodium ions (WNaþ) is approximately 70%. The composition of the post-filtration liquid, after filtering out NaHCO3, as calculated for 1 ton of the produced sodium carbonate, is 283 kg NH4HCO3, 155 kg (NH4)2CO3, 24.3 kg NaHCO3, 1009 kg NH4Cl and 432 kg NaCl. In the first step that liquid is subjected to the diaphragm regeneration, and subsequently treated with the suspension of lime milk and water steam to obtain NH3 which is re-directed to the process after its loses are supplemented with fresh NH3 ski et al., 1978; Steinhauser, 2008; Bortel and Koneczny, (Niederlin 1992; Van den Berg & de Jong, 1980; Kasikowski et al., 2004). The amount of liquid waste from the process of ammonia regeneration exceeds the amount of the produced soda by the factor of 10. The major components are the unreacted NaCl and
* Corresponding author. Tel.: þ48 566114569; fax: þ48 566542477. E-mail address: [email protected] (M. Trypu c). 0959-6526/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2010.11.009
CaCl2 in the amounts equivalent to the decomposed NH4Cl, and these salts in total are directed to the open water basins. It has to be emphasized, that each year during production of 1 million ton of sodium carbonate, the liquid waste contains 432 000 ton of ski et al., 1978). unreacted NaCl and 1 047 000 ton CaCl2 (Niederlin The progressive degradation of the natural environment, the climate warm-up and large amounts of community and industrial waste indicate that the environment protection is the major challenge of the XXI century. The major goal of the EU countries is a balanced economy growth, taking into account the needs of protection of the natural environment and using the pro-ecological and pro-environmental technologies (Khan, 2008; Costa et al., 2010; Nash, 2009). Due to the advancing environment pollution and depleting natural resources, it is necessary to recycle the intermediate products, by-products, recycling materials and waste materials, including those considered dangerous. Most of the industrial waste is currently considered as the re-usable substances and the source of valuable materials. The procedures of obtaining calcium carbonate, both technical, modified for the use as a filling material and that of a large packing density for the pharmacy use, are known from the literature (Sawada, 1997; Trypu c and Buczkowski, 1991; Trypu c et al., 1999; Kitamura, 2001; Domka, 1994; Pavez et al., 2005). Calcium carbonate is obtained in a reaction of the waste post-distillation liquid generated in the Solvay process with the post-crystallization liquor from the division of baking soda production or with the solution of sodium bicarbonate, at the temperature not exceeding 323 K. The disadvantage of these processes is that the post-
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filtration liquid generated after filtering off CaCO3 and containing mainly NaCl, is directed to the open water basins, therefore negatively affecting the natural environment. The usage of either Na2CO3, NaHCO3 or carbon(IV) oxide generated in the decomposition of limestone, for the process of precipitation of calcium carbonate negatively affects the economical parameters of the ski et al., 1978; Solvay method of the soda production (Niederlin Steinhauser, 2008; Bortel and Koneczny, 1992; Van den Berg & de Jong, 1980; Kasikowski et al., 2004; Khan, 2008). The paper proposes the method of complete elimination of the chloride ion discharge into the open water basins after the process of CaCO3 precipitation. In the proposed method of CaCO3 precipitation, the source of the carbonate ions will be the post-filtration liquid obtained after filtration of the NaHCO3 precipitate, while the source of calcium ions will be the liquid generated from the division of the ammonia regeneration. Therefore, in the proposed method the post-filtration liquid (after CaCO3 filtration) will contain only NH4Cl in an amount equivalent to that of NaHCO3 precipitated during carbonization of the ammoniated brine, the additional amount of NH4Cl generated in a process of precipitation of CaCO3 from NH4HCO3, as well as (NH4)2CO3 and unreacted NaCl (Trypu c et al.,2009). That solution will be the main source of the solid NH4Cl obtained in a process of evaporation and fractional crystallization. Solid NaCl also obtained in that process might be either recycled into the Solvay process for preparation of brine, or used in other branches of industry. That will assure the complete use of chloride ions, which up to date are directed to the natural water reservoirs as a waste. Precipitation of CaCO3 from the post-filtration solution leads to 2 the complete utilization of HCO 3 and CO3 ions. The process does not require additional heating, necessary for decomposition of the unstable ammonium salts. During the precipitation, they are converted into equivalent amount of NH4Cl, increasing its initial concentration resulting from the reaction of the reciprocal exchange salts pair system: NaCl þ NH4HCO3 4 NaHCO3 þ NH4Cl
(1)
The above process is advantageous for obtaining NH4Cl from the solution remaining after CaCO3 filtration. An additional advantage is the way of obtaining the precipitated calcium carbonate at temperatures not exceeding 323 K. That allows to obtain chalk of desired physico-chemical properties due to easy control of the process conditions during precipitation (the sequence of dosage, the reagents concentration and the dose rate, an introduction of crystal nuclei into the reactor). Another advantage of the proposed method is the utilization of the condensate obtained after separation of NH4Cl and NaCl sediments in removal of the chloride ions from the precipitated CaCO3, which allows to replace the demineralized water used so far. Both the literature reports and our research (Sawada, 1997; Wypych, 2000; Demjen et al., 1997; Bia1owicz et al., 2008; Hirasawa, 2000; Hostomsky and Jones, 1991) revealed that the physico-chemical properties of the obtained CaCO3 depend on the conditions of the precipitation process. It has to be stated that different branches of industry using calcium carbonate have different requirements for its purity, granulation, bulk density and other. The reported research focuses on obtaining calcium carbonate from the post-distillation liquid (DS) being a waste from the ammonia regeneration node of a Solvay method. Since the concentration of Ca2þ ions in DS is stable, that solution might be used as one of the basic reagents. The source of carbonate and ammonium ions for the method might be a post-filtration solution obtained after
filtering off the NaHCO3 precipitate. Research was conducted at 303 K, because of decomposition of volatile ammonium salts at higher temperatures. The effect of reagent dosage time and concentration on the physico-chemical properties of the obtained product was investigated. For the obtained samples of calcium carbonate, different parameters have been investigated, including the bulk and packing densities, the absorption capacities of water, paraffin oil and dibutyl phthalate, as well as the distribution of crystal size and the crystal form. To determine the morphology and microstructure of the particles, the SEM microscopy, thermal analysis and X-ray diffraction methods have been used. 2. Experimental section 2.1. Reagents The post-distillation liquid (DS) and the post-filtration lye have been used for precipitation of calcium carbonate. Both have been obtained from Janikowo Soda Plant Janikosoda S.A (Poland). The post-distillation liquid DS is generated in the ammonia regeneration node in the Solvay method. That liquid contains calcium chloride and sodium chloride. The impurities are sulfate ions and solid particles. The basic requirement for the possibility of use of that liquid for obtaining the precipitated calcium carbonate was its purification from the solid components by clarification and filtration. The post-filtration lye generated in a process of sodium carbonate production after filtration of the NaHCO3 sediment, contains ammonium carbonate and bicarbonate, sodium bicarbonate, sodium chloride and ammonium chloride. The average composition of the post-filtration lye and the DS liquid is presented in Table 1. 2.2. Methods Investigation of the process of sedimentation of calcium carbonate was conducted at 303 K in the apparatus presented on Fig. 1. Temperature was controlled with the mercury thermometers, time of the reagents dosage was regulated with the pre-calibrated peristaltic pump. During the experiments, the constant stirring rate of the reaction mixture was kept at 500 rotations per min. Research was divided into three stages. In the first stage the DS and post-filtration lye were used, and their composition is presented in Table 1. Precipitation of calcium carbonate was performed with the use of 400 cm3 of the DS liquid and the equivalent amount of post-filtration lye (according to Equation (2)). The reaction gave approximately 30 g of the product. To obtain the amount of CaCO3 Table 1 The average composition of post-filtration liquid and after distillation liquid. Component
c (mol/dm3)
Post-distillation liquid (DS) Ca2þ Naþ Fe3þeFe2þ Cl SO2 4 pH ¼ 10.0e10.05
1.064 0.952 8.92 104 2.931 0.023
Post-filtration liquid CO2 3 NHþ 4 Cl Fe3þeFe2þ SO2 4
0.690 4.962 4.389 5.92 103 0.012
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as well as water, the absorption capacities of paraffin oil and dibutyl phthalate. The crystal structure of the precipitated calcium carbonate was investigated with the Scanning Electron Microscopy SEM and X-ray powder diffraction. Morphology and crystal structure of the obtained samples were determined with SEM LEO 1430VP. Based on these results, the geometrical form of the conglomerates and shape of the crystals were determined. The qualitative analysis of the precipitated calcium carbonate was performed with the X-ray diffraction method on a Philips X-Pert PRO powder diffractometer. For the obtained samples of the precipitated calcium carbonate, the size of particles and its distribution were determined with the use of the diffraction of the laser beam on a Mastersizer 2000 apparatus. Samples were dispersed in water and the Hydro 2000G device was used. For each sample, water was introduced to the device tank to determine the electrical and optical background level, then the sample was added and the experiment was performed. 2.3. Analytical methods
Fig. 1. Schematic diagram of apparatus used for calcium carbonate obtaining: 1 e lower reactor, 2 e upper reactor, 3 e stirrer, 4 e thermometer, 5 eperistaltic pump, 6 e thermostat, 7 e outlet valve.
necessary for the physico-chemical analyses, each experiment was performed two times. Ca2þ þ CO2 3 / CaCO3
(2)
The DS liquid was dosed into the lower reactor (1) and the postfiltration lye into the upper reactor (2) (Fig. 1), and thermostated to reach 303 K. Subsequently, the post-filtration lye was dosed at the selected time 2, 5, 10, 20 and 30 min into the DS liquid. The postreaction suspension was kept in the reactor for additional 30 min while maintaining the stirring rate. Then, it was transferred into the settler for the sedimentation. The precipitate of calcium carbonate obtained by the separation of the clear remains, was filtered with the sintered glass crucible and washed with the distilled water to remove chloride ions. The obtained precipitate was dried at 378 K and subjected to physico-chemical analyses. In the second stage of the research, the precipitated chalk was obtained with the use of the undiluted DS liquid and the post-filtration lye diluted with water in a volume proportion 1:1, 2:1 and 3:1. In the last series of experiments, the post-filtration lye was used without dilution, while the DS liquid was diluted with water in a volume ratio 2:1 and 4:1. Precipitation of CaCO3 with the use of the diluted solutions was analogous to that for the concentrated solutions. The use of solutions with different concentrations assures the range of different supersaturation conditions in a process of calcium carbonate precipitation. The use of concentrated solutions results in the supersaturation relative to calcium ions, which is several hundred times larger than that in the equilibrium state. In such case the precipitation of CaCO3 proceeds in a totally uncontrolled way. Dilution of reagents ensures the radical lowering of supersaturation and obtaining of the product of different particle size (Rojkowski and Synowiec, 1991). The following physico-chemical parameters of the obtained calcium carbonate were investigated: the bulk and packing densities
Concentration of calcium ions in the DS liquid was determined by a complexometric titration with the EDTA solutions (Hermanowicz, 1999). Concentration of carbonate ions in the post-filtration lye was determined potentiometrically by titration with 0.1 M HCl (Minczewski and Marczenko, 1987), using the 716 DMS TITRINO automated titrator and the glass electrode of Methrom, Switzerland. The Fe(III) concentration in substrates was determined spectrophotometrically with the double-beam Hitachi U-2000 UV/Vis spectrophotometer. The applied method was based on the ability of Fe3þ ions to form a complex with sulfosalicylic acid (Hermanowicz, 1999). The gravimetric method was used for determination of SO2 4 ski, 1982). Concentration of chloride ions was ions (Struszyn determined with the Mohr method (Minczewski and Marczenko, 1987; Williams, 1985). The potentiometric titration was performed with the 716 DMS TITRINO titrator. Concentration of sodium ions was determined with the gravimetric method of I. M. Kolthoff and H. H. Barber, in a form of sodiumezinceuranyl acetate (Furman, 1962). 3. Results and discussion Table 2 presents the properties of calcium carbonate precipitated at 303 K for different time of dosage of undiluted reagents, as well as for different levels of dilution of the post-filtration lye and the DS liquid. The data include the bulk density and packing density, as well as absorption capacities of water (Hw), paraffin oil (Ho) and dibutyl phthalate (Hf). The last column presents an average particle diameter calculated for the whole volume of the sample. That value was estimated as one of the parameters during determination of distribution of the CaCO3 particle size by the laser beam diffraction method. Analysis of the obtained data indicates that for the concentrated solutions of substrates, the bulk density and packing density increase with the increasing time of dosage of the post-filtration lye into the DS liquid. The bulk density of the obtained chalk is in the range 715e770 g dm3, while the packing density is 910e960 g dm3. The other important parameters determining the possible use of the obtained calcium carbonate are absorption capacities of water, paraffin oil and dibutyl phthalate. The amount of water and oil absorbed by the calcium carbonate samples characterize the hydrophilic and hydrophobic properties of the product and the degree of the crystals agglomeration. Data in Table 2 indicates that absorptiveness of all media decreases with the increasing time of the lye dosage. Analysis revealed that the changes in the water, oil
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Table 2 Physico-chemical parameters of calcium carbonate precipitated from post-filtration liquid and post-distillation liquid at 303 K. Absorbing capacities (cm3/100 g)
Time of reagent Density dosage (min) (g/dm3) Bulk 2 5 10 20 30
715 721 730 741 770
Average size of particles (mm)
Packing Water Paraffin Dibutyl oil phthalate 910 923 943 953 960
68 66 65 63 60
76 72 70 66 64
71 69 68 65 62
26.06 27.02 35.60 40.98 48.30
Post-filtration liquid:H2O 1:1 2 700 900 5 740 929 10 790 953 20 800 972 30 870 1000
65 61 60 59 58
71 68 63 61 60
64 63 62 60 57
28.15 32.93 22.67 39.01 21.30
Post-filtration liquid:H2O 2:1 2 667 800 5 697 870 10 741 1000 20 741 1000 30 833 1250
77 68 57 56 52
80 74 65 63 58
78 71 63 60 56
37.15 32.77 30.81 35.37 31.99
Post-filtration liquid:H2O 3:1 2 870 1000 5 909 1000 10 1000 1111 20 1053 1083 30 1212 1290
57 56 52 48 41
62 61 60 57 51
60 59 54 50 45
71.30 61.62 52.25 63.17 63.84
DS:H2O 2:1 2 5 10 20 30
741 741 800 869 909
930 1000 1000 1052 1054
66 62 60 56 53
69 65 63 60 60
65 63 62 58 59
30.02 36.75 32.18 32.47 37.78
DS:H2O 4:1 2 5 10 20 30
770 770 869 890 954
976 1000 1052 1053 1112
68 64 55 54 52
76 70 61 60 57
70 67 59 56 54
32.82 43.75 40.21 32.16 41.53
and dibutyl phthalate absorption capacities are inversely proportional to the bulk and packing densities of calcium carbonate samples obtained from the concentrated substrates. The Hw are in the range 68e60 cm3/100 g, the Ho values range 76e64 cm3/100 g, and Hf values are 71e62 cm3/100 g. It is clear that for the constant time of the reagent dosage, the values of absorbing capacity of dibutyl phthalate are intermediate between those of paraffin oil and water.
Table 3 The interplanar distances, intensities of the diffracted beams and the Bragg angles for calcite and vaterite standards. Calcite
Vaterite
d [A]
2Theta [deg]
I [%]
d [A]
2Theta [deg]
I [%]
3.84000 3.02000 2.49000 2.28000 2.09000 1.92000 1.87000 1.62000 1.60000 1.52000 1.51000 1.47000 1.44000 1.42000 1.36000 1.33000 1.29000 1.24000 1.18000 1.15000 1.14000
23.144 29.555 36.041 39.492 43.254 47.306 48.652 56.783 57.559 60.899 61.345 63.204 64.678 65.703 68.999 70.785 73.330 76.809 81.506 84.107 85.017
60.0 100.0 60.0 70.0 70.0 90.0 80.0 40.0 50.0 60.0 12.0 40.0 50.0 40.0 10.0 40.0 30.0 20.0 40.0 40.0 40.0
4.26000 3.58000 3.29000 2.73000 2.31000 2.06000 1.87000 1.83000 1.82000 1.65000 1.55000 1.54000 1.48000 1.37000 1.32000 1.29000 1.15000 1.11000
20.835 24.851 27.081 32.778 38.958 43.917 48.652 49.787 50.079 55.660 59.599 60.026 62.728 68.425 71.403 73.330 84.107 87.889
13.0 63.0 75.0 100.0 8.0 63.0 15.0 63.0 20.0 31.0 8.0 20.0 8.0 8.0 10.0 13.0 8.0 5.0
Analysis of data from the second stage of research (different dilutions of the post-filtration lye) reveals that for each series of experiments the increasing time of the lye dosage into the DS liquid results in the increase of both bulk and packing densities. Water, oil and dibutyl phthalate absorption capacities decrease with the increasing values of the bulk density for each level of dilution of the post-filtration liquid. The highest values of the bulk and packing densities are found for 3:1 ratio of the lye dilution with water. The bulk density for that series of experiments is in the range 870e1212 g dm3, while the packing density is 1000e1290 g dm3. The physico-chemical properties of calcium carbonate obtained with the use of the diluted DS liquid are analogous to those obtained in other series of experiments. In each series, the elongation of time of the lye dosage into DS results in increasing values of bulk and packing densities and in the decrease of all media absorption capacities. Similar to the effect of the dilution of the post-filtration lye, the use of the diluted DS liquid increases the packing density of the obtained calcium carbonate in comparison to those determined for chalk obtained from the concentrated solutions. The values of the packing density for chalk obtained from the diluted DS liquid are 930e1112 g dm3.
Fig. 2. Particle size distribution and SEM photo of obtained calcium carbonate (post-filtration liquid:H2O 3:1, t ¼ 30 min).
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Fig. 3. Diffraction pattern of calcium carbonate sample with the lowest bulk density.
Analysis of the distribution of the particle size for the obtained calcium carbonate revealed that the crystal size for all samples ranges from 0.316 to 208.930 mm. The size of particles for most samples is in the range 0.316e120.226 mm. The exception is a series in which CaCO3 was precipitated with the diluted post-filtration lye (3:1), with the crystal size in the range 4.365e208.930 mm. That is reflected in the largest values of the crystal diameters calculated for the whole sample volume, as presented in Table 2. Analysis of the distribution of the particle size indicated that the diameter of particles of the obtained CaCO3 decreases with the increasing dilution of the post-filtration lye. The largest particles were obtained with the 3:1 dilution of the lye with water. That results in the largest bulk density. Analogous dependence was found for precipitation of CaCO3 with the diluted DS liquid.
For the selected sample, the distribution of the particle size and the picture from the scanning electron microscopy are presented on Fig. 2. Parameters d(0,1), d(0,5), d(0,9) are the standard values in % and indicate respectively: e d(0,1) particle size [mm] which is larger than the size for 10% of particles in the sample, e d(0,5) particle size [mm] which is larger than the size for 50% of particles in the sample, e d(0,9) particle size [mm] which is larger than the size for 90% of particles in the sample. Parameter d(4,3) indicates the average diameter of the particles as calculated for the whole volume of the sample.
Fig. 4. Example of the EDXRF spectrum for the obtained calcium carbonate.
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The microscopic research revealed that the obtained chalk has a significant tendency to agglomerate. Therefore the dense system of agglomerates of diverse geometrical form was observed and only small amount of single crystals was detected. The qualitative analysis of the precipitated calcium carbonate was performed with the XRD method using the polycrystalline powder samples. The X-ray analyses of the solid phases were based on the distribution curves of the dispersed radiation intensity I ¼ f (q). For each diffraction pattern, the series of interplanar distances (d) and relative intensities (I) were given and compared with data for the respective standards. The characteristic interplanar distances, intensities of the diffracted beams and the Bragg angles for the standards (calcite and vaterite) are presented in Table 3. Fig. 3 presents the typical diffractogram for the sample of precipitated calcium carbonate. Based on the X-ray diffraction (Fig. 3) and the SEM pictures, it was found that calcium carbonate is precipitated in two polymorphic forms e calcite and vaterite. Calcite is the most abundant and very stable polymorphic form of calcium carbonate. Vaterite is the most rare crystal form of CaCO3. It is unstable and undergoes the transformation into calcite. Analysis of the selected samples of calcium carbonate was performed with the scanning electron microscopy. In all investigated samples, most crystals were found in a form of agglomerates of different geometrical form. Samples of chalk with lower bulk density revealed the relatively high amount of single crystals, while in samples of high bulk density a relatively high amount of agglomerates was detected. In the investigated samples, most crystals were of a rhombic shape, characteristic for calcite, as well as the spherical shape corresponding to vaterite. However, the needle form crystals characteristic for aragonite, were not found. The typical SEM picture is presented on Fig. 2. Additionally, to determine the purity of the obtained calcium carbonate, the qualitative analysis of the samples was performed using EDXRF method (Brouwer, 2006). In this method, the sample is irradiated with X-rays emitted by an X-ray tube and the resulting characteristic X-rays generated in the sample (fluorescent X-rays) are detected. By measuring the energies of the radiation emitted by the sample, it is possible to determine what elements are present (qualitative analysis). By measuring the intensities of the emitted energies it is possible to determine how much of each element is present in the sample (quantitative analysis). Analyses were performed with the MiniPal4 PANalytical compact energy dispersive X-ray spectrometer. It was found that the purity of the obtained product is larger than 99%, and the impurities are: Al2O3 (0.28e0.34%), SO3 (0.39e0.54%), Fe2O3 (0.10e0.11%). The example of the obtained EDXRF spectra is presented on Fig. 4. 4. Conclusions CaCO3 from the post-distillation liquid DS and post-filtration liquid from Solvay method of the soda production at 303 K was synthesised. Analysis of data reveals that for each series of experiments the increasing time of the lye dosage into the DS liquid results in the increase of both bulk and packing densities. Absorption capacities for water, oil and dibutyl phthalate decreases with the increasing values of the bulk density. The highest values of the bulk and packing densities are found for 3:1 ratio of the post-filtration liquid dilution with water. CaCO3 obtained for 30 min time of dosage showed the highest bulk
(1212 g dm3) and packing (1290 g dm3) densities. For this sample, the absorption capacities of water, paraffin oil and dibutyl phthalate are the lowest. Formation of agglomerates and only small amount of single crystals was observed. Calcite and vaterite structures of the crystals were evidenced by XRD and SEM.
Acknowledgments The research was financed as the research project MNiSW NN 205 104 135 from the Polish Ministry for Science and Higher Education (2008e2011).
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CaCO3 production using liquid waste from Solvay method Mieczys1aw Trypu c*, Katarzyna Bia1owicz , Poland Nicolaus Copernicus University, Faculty of Chemistry, Department of Chemical Technology, Gagarina 7, 87-100 Torun
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 March 2010 Received in revised form 9 November 2010 Accepted 12 November 2010 Available online 8 December 2010
Process of obtaining CaCO3 from the waste post-distillation liquid DS and post-filtration liquid from Solvay method of the soda production at 303 K was investigated. Reagents were dosed in a stoichiometric ratio without dilution, for different concentrations of the DS and post-filtration liquids. The dosage time was varied in the range 2e30 min, the reagent stirring rate was 500 rpm. For the obtained samples of CaCO3, the bulk and packing densities, water, paraffin oil and dibutyl phthalate absorption capacities, distribution of the particle size as well as the crystalline form were determined. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Solvay method Calcium carbonate Post-distillation liquor (DS) Post-filtration liquid Bulk density Packing density
1. Introduction In the EU countries, the calcinated soda is produced exclusively with the Solvay method, due to the general availability and relatively low prices of the substrates used. Besides numerous advantages, the Solvay method has many disadvantages. It is characterized by low material and energy efficiency and high noxiousness for the natural environment. The energy costs constitute 33% of the overall costs, while the degree of utilization of limestone and coke is 69 and 53%, respectively. The basic step of that method is carbonization of the ammoniated brine, for which the average efficiency calculated relatively to the sodium ions (WNaþ) is approximately 70%. The composition of the post-filtration liquid, after filtering out NaHCO3, as calculated for 1 ton of the produced sodium carbonate, is 283 kg NH4HCO3, 155 kg (NH4)2CO3, 24.3 kg NaHCO3, 1009 kg NH4Cl and 432 kg NaCl. In the first step that liquid is subjected to the diaphragm regeneration, and subsequently treated with the suspension of lime milk and water steam to obtain NH3 which is re-directed to the process after its loses are supplemented with fresh NH3 ski et al., 1978; Steinhauser, 2008; Bortel and Koneczny, (Niederlin 1992; Van den Berg & de Jong, 1980; Kasikowski et al., 2004). The amount of liquid waste from the process of ammonia regeneration exceeds the amount of the produced soda by the factor of 10. The major components are the unreacted NaCl and
* Corresponding author. Tel.: þ48 566114569; fax: þ48 566542477. E-mail address: [email protected] (M. Trypu c). 0959-6526/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2010.11.009
CaCl2 in the amounts equivalent to the decomposed NH4Cl, and these salts in total are directed to the open water basins. It has to be emphasized, that each year during production of 1 million ton of sodium carbonate, the liquid waste contains 432 000 ton of ski et al., 1978). unreacted NaCl and 1 047 000 ton CaCl2 (Niederlin The progressive degradation of the natural environment, the climate warm-up and large amounts of community and industrial waste indicate that the environment protection is the major challenge of the XXI century. The major goal of the EU countries is a balanced economy growth, taking into account the needs of protection of the natural environment and using the pro-ecological and pro-environmental technologies (Khan, 2008; Costa et al., 2010; Nash, 2009). Due to the advancing environment pollution and depleting natural resources, it is necessary to recycle the intermediate products, by-products, recycling materials and waste materials, including those considered dangerous. Most of the industrial waste is currently considered as the re-usable substances and the source of valuable materials. The procedures of obtaining calcium carbonate, both technical, modified for the use as a filling material and that of a large packing density for the pharmacy use, are known from the literature (Sawada, 1997; Trypu c and Buczkowski, 1991; Trypu c et al., 1999; Kitamura, 2001; Domka, 1994; Pavez et al., 2005). Calcium carbonate is obtained in a reaction of the waste post-distillation liquid generated in the Solvay process with the post-crystallization liquor from the division of baking soda production or with the solution of sodium bicarbonate, at the temperature not exceeding 323 K. The disadvantage of these processes is that the post-
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filtration liquid generated after filtering off CaCO3 and containing mainly NaCl, is directed to the open water basins, therefore negatively affecting the natural environment. The usage of either Na2CO3, NaHCO3 or carbon(IV) oxide generated in the decomposition of limestone, for the process of precipitation of calcium carbonate negatively affects the economical parameters of the ski et al., 1978; Solvay method of the soda production (Niederlin Steinhauser, 2008; Bortel and Koneczny, 1992; Van den Berg & de Jong, 1980; Kasikowski et al., 2004; Khan, 2008). The paper proposes the method of complete elimination of the chloride ion discharge into the open water basins after the process of CaCO3 precipitation. In the proposed method of CaCO3 precipitation, the source of the carbonate ions will be the post-filtration liquid obtained after filtration of the NaHCO3 precipitate, while the source of calcium ions will be the liquid generated from the division of the ammonia regeneration. Therefore, in the proposed method the post-filtration liquid (after CaCO3 filtration) will contain only NH4Cl in an amount equivalent to that of NaHCO3 precipitated during carbonization of the ammoniated brine, the additional amount of NH4Cl generated in a process of precipitation of CaCO3 from NH4HCO3, as well as (NH4)2CO3 and unreacted NaCl (Trypu c et al.,2009). That solution will be the main source of the solid NH4Cl obtained in a process of evaporation and fractional crystallization. Solid NaCl also obtained in that process might be either recycled into the Solvay process for preparation of brine, or used in other branches of industry. That will assure the complete use of chloride ions, which up to date are directed to the natural water reservoirs as a waste. Precipitation of CaCO3 from the post-filtration solution leads to 2 the complete utilization of HCO 3 and CO3 ions. The process does not require additional heating, necessary for decomposition of the unstable ammonium salts. During the precipitation, they are converted into equivalent amount of NH4Cl, increasing its initial concentration resulting from the reaction of the reciprocal exchange salts pair system: NaCl þ NH4HCO3 4 NaHCO3 þ NH4Cl
(1)
The above process is advantageous for obtaining NH4Cl from the solution remaining after CaCO3 filtration. An additional advantage is the way of obtaining the precipitated calcium carbonate at temperatures not exceeding 323 K. That allows to obtain chalk of desired physico-chemical properties due to easy control of the process conditions during precipitation (the sequence of dosage, the reagents concentration and the dose rate, an introduction of crystal nuclei into the reactor). Another advantage of the proposed method is the utilization of the condensate obtained after separation of NH4Cl and NaCl sediments in removal of the chloride ions from the precipitated CaCO3, which allows to replace the demineralized water used so far. Both the literature reports and our research (Sawada, 1997; Wypych, 2000; Demjen et al., 1997; Bia1owicz et al., 2008; Hirasawa, 2000; Hostomsky and Jones, 1991) revealed that the physico-chemical properties of the obtained CaCO3 depend on the conditions of the precipitation process. It has to be stated that different branches of industry using calcium carbonate have different requirements for its purity, granulation, bulk density and other. The reported research focuses on obtaining calcium carbonate from the post-distillation liquid (DS) being a waste from the ammonia regeneration node of a Solvay method. Since the concentration of Ca2þ ions in DS is stable, that solution might be used as one of the basic reagents. The source of carbonate and ammonium ions for the method might be a post-filtration solution obtained after
filtering off the NaHCO3 precipitate. Research was conducted at 303 K, because of decomposition of volatile ammonium salts at higher temperatures. The effect of reagent dosage time and concentration on the physico-chemical properties of the obtained product was investigated. For the obtained samples of calcium carbonate, different parameters have been investigated, including the bulk and packing densities, the absorption capacities of water, paraffin oil and dibutyl phthalate, as well as the distribution of crystal size and the crystal form. To determine the morphology and microstructure of the particles, the SEM microscopy, thermal analysis and X-ray diffraction methods have been used. 2. Experimental section 2.1. Reagents The post-distillation liquid (DS) and the post-filtration lye have been used for precipitation of calcium carbonate. Both have been obtained from Janikowo Soda Plant Janikosoda S.A (Poland). The post-distillation liquid DS is generated in the ammonia regeneration node in the Solvay method. That liquid contains calcium chloride and sodium chloride. The impurities are sulfate ions and solid particles. The basic requirement for the possibility of use of that liquid for obtaining the precipitated calcium carbonate was its purification from the solid components by clarification and filtration. The post-filtration lye generated in a process of sodium carbonate production after filtration of the NaHCO3 sediment, contains ammonium carbonate and bicarbonate, sodium bicarbonate, sodium chloride and ammonium chloride. The average composition of the post-filtration lye and the DS liquid is presented in Table 1. 2.2. Methods Investigation of the process of sedimentation of calcium carbonate was conducted at 303 K in the apparatus presented on Fig. 1. Temperature was controlled with the mercury thermometers, time of the reagents dosage was regulated with the pre-calibrated peristaltic pump. During the experiments, the constant stirring rate of the reaction mixture was kept at 500 rotations per min. Research was divided into three stages. In the first stage the DS and post-filtration lye were used, and their composition is presented in Table 1. Precipitation of calcium carbonate was performed with the use of 400 cm3 of the DS liquid and the equivalent amount of post-filtration lye (according to Equation (2)). The reaction gave approximately 30 g of the product. To obtain the amount of CaCO3 Table 1 The average composition of post-filtration liquid and after distillation liquid. Component
c (mol/dm3)
Post-distillation liquid (DS) Ca2þ Naþ Fe3þeFe2þ Cl SO2 4 pH ¼ 10.0e10.05
1.064 0.952 8.92 104 2.931 0.023
Post-filtration liquid CO2 3 NHþ 4 Cl Fe3þeFe2þ SO2 4
0.690 4.962 4.389 5.92 103 0.012
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as well as water, the absorption capacities of paraffin oil and dibutyl phthalate. The crystal structure of the precipitated calcium carbonate was investigated with the Scanning Electron Microscopy SEM and X-ray powder diffraction. Morphology and crystal structure of the obtained samples were determined with SEM LEO 1430VP. Based on these results, the geometrical form of the conglomerates and shape of the crystals were determined. The qualitative analysis of the precipitated calcium carbonate was performed with the X-ray diffraction method on a Philips X-Pert PRO powder diffractometer. For the obtained samples of the precipitated calcium carbonate, the size of particles and its distribution were determined with the use of the diffraction of the laser beam on a Mastersizer 2000 apparatus. Samples were dispersed in water and the Hydro 2000G device was used. For each sample, water was introduced to the device tank to determine the electrical and optical background level, then the sample was added and the experiment was performed. 2.3. Analytical methods
Fig. 1. Schematic diagram of apparatus used for calcium carbonate obtaining: 1 e lower reactor, 2 e upper reactor, 3 e stirrer, 4 e thermometer, 5 eperistaltic pump, 6 e thermostat, 7 e outlet valve.
necessary for the physico-chemical analyses, each experiment was performed two times. Ca2þ þ CO2 3 / CaCO3
(2)
The DS liquid was dosed into the lower reactor (1) and the postfiltration lye into the upper reactor (2) (Fig. 1), and thermostated to reach 303 K. Subsequently, the post-filtration lye was dosed at the selected time 2, 5, 10, 20 and 30 min into the DS liquid. The postreaction suspension was kept in the reactor for additional 30 min while maintaining the stirring rate. Then, it was transferred into the settler for the sedimentation. The precipitate of calcium carbonate obtained by the separation of the clear remains, was filtered with the sintered glass crucible and washed with the distilled water to remove chloride ions. The obtained precipitate was dried at 378 K and subjected to physico-chemical analyses. In the second stage of the research, the precipitated chalk was obtained with the use of the undiluted DS liquid and the post-filtration lye diluted with water in a volume proportion 1:1, 2:1 and 3:1. In the last series of experiments, the post-filtration lye was used without dilution, while the DS liquid was diluted with water in a volume ratio 2:1 and 4:1. Precipitation of CaCO3 with the use of the diluted solutions was analogous to that for the concentrated solutions. The use of solutions with different concentrations assures the range of different supersaturation conditions in a process of calcium carbonate precipitation. The use of concentrated solutions results in the supersaturation relative to calcium ions, which is several hundred times larger than that in the equilibrium state. In such case the precipitation of CaCO3 proceeds in a totally uncontrolled way. Dilution of reagents ensures the radical lowering of supersaturation and obtaining of the product of different particle size (Rojkowski and Synowiec, 1991). The following physico-chemical parameters of the obtained calcium carbonate were investigated: the bulk and packing densities
Concentration of calcium ions in the DS liquid was determined by a complexometric titration with the EDTA solutions (Hermanowicz, 1999). Concentration of carbonate ions in the post-filtration lye was determined potentiometrically by titration with 0.1 M HCl (Minczewski and Marczenko, 1987), using the 716 DMS TITRINO automated titrator and the glass electrode of Methrom, Switzerland. The Fe(III) concentration in substrates was determined spectrophotometrically with the double-beam Hitachi U-2000 UV/Vis spectrophotometer. The applied method was based on the ability of Fe3þ ions to form a complex with sulfosalicylic acid (Hermanowicz, 1999). The gravimetric method was used for determination of SO2 4 ski, 1982). Concentration of chloride ions was ions (Struszyn determined with the Mohr method (Minczewski and Marczenko, 1987; Williams, 1985). The potentiometric titration was performed with the 716 DMS TITRINO titrator. Concentration of sodium ions was determined with the gravimetric method of I. M. Kolthoff and H. H. Barber, in a form of sodiumezinceuranyl acetate (Furman, 1962). 3. Results and discussion Table 2 presents the properties of calcium carbonate precipitated at 303 K for different time of dosage of undiluted reagents, as well as for different levels of dilution of the post-filtration lye and the DS liquid. The data include the bulk density and packing density, as well as absorption capacities of water (Hw), paraffin oil (Ho) and dibutyl phthalate (Hf). The last column presents an average particle diameter calculated for the whole volume of the sample. That value was estimated as one of the parameters during determination of distribution of the CaCO3 particle size by the laser beam diffraction method. Analysis of the obtained data indicates that for the concentrated solutions of substrates, the bulk density and packing density increase with the increasing time of dosage of the post-filtration lye into the DS liquid. The bulk density of the obtained chalk is in the range 715e770 g dm3, while the packing density is 910e960 g dm3. The other important parameters determining the possible use of the obtained calcium carbonate are absorption capacities of water, paraffin oil and dibutyl phthalate. The amount of water and oil absorbed by the calcium carbonate samples characterize the hydrophilic and hydrophobic properties of the product and the degree of the crystals agglomeration. Data in Table 2 indicates that absorptiveness of all media decreases with the increasing time of the lye dosage. Analysis revealed that the changes in the water, oil
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Table 2 Physico-chemical parameters of calcium carbonate precipitated from post-filtration liquid and post-distillation liquid at 303 K. Absorbing capacities (cm3/100 g)
Time of reagent Density dosage (min) (g/dm3) Bulk 2 5 10 20 30
715 721 730 741 770
Average size of particles (mm)
Packing Water Paraffin Dibutyl oil phthalate 910 923 943 953 960
68 66 65 63 60
76 72 70 66 64
71 69 68 65 62
26.06 27.02 35.60 40.98 48.30
Post-filtration liquid:H2O 1:1 2 700 900 5 740 929 10 790 953 20 800 972 30 870 1000
65 61 60 59 58
71 68 63 61 60
64 63 62 60 57
28.15 32.93 22.67 39.01 21.30
Post-filtration liquid:H2O 2:1 2 667 800 5 697 870 10 741 1000 20 741 1000 30 833 1250
77 68 57 56 52
80 74 65 63 58
78 71 63 60 56
37.15 32.77 30.81 35.37 31.99
Post-filtration liquid:H2O 3:1 2 870 1000 5 909 1000 10 1000 1111 20 1053 1083 30 1212 1290
57 56 52 48 41
62 61 60 57 51
60 59 54 50 45
71.30 61.62 52.25 63.17 63.84
DS:H2O 2:1 2 5 10 20 30
741 741 800 869 909
930 1000 1000 1052 1054
66 62 60 56 53
69 65 63 60 60
65 63 62 58 59
30.02 36.75 32.18 32.47 37.78
DS:H2O 4:1 2 5 10 20 30
770 770 869 890 954
976 1000 1052 1053 1112
68 64 55 54 52
76 70 61 60 57
70 67 59 56 54
32.82 43.75 40.21 32.16 41.53
and dibutyl phthalate absorption capacities are inversely proportional to the bulk and packing densities of calcium carbonate samples obtained from the concentrated substrates. The Hw are in the range 68e60 cm3/100 g, the Ho values range 76e64 cm3/100 g, and Hf values are 71e62 cm3/100 g. It is clear that for the constant time of the reagent dosage, the values of absorbing capacity of dibutyl phthalate are intermediate between those of paraffin oil and water.
Table 3 The interplanar distances, intensities of the diffracted beams and the Bragg angles for calcite and vaterite standards. Calcite
Vaterite
d [A]
2Theta [deg]
I [%]
d [A]
2Theta [deg]
I [%]
3.84000 3.02000 2.49000 2.28000 2.09000 1.92000 1.87000 1.62000 1.60000 1.52000 1.51000 1.47000 1.44000 1.42000 1.36000 1.33000 1.29000 1.24000 1.18000 1.15000 1.14000
23.144 29.555 36.041 39.492 43.254 47.306 48.652 56.783 57.559 60.899 61.345 63.204 64.678 65.703 68.999 70.785 73.330 76.809 81.506 84.107 85.017
60.0 100.0 60.0 70.0 70.0 90.0 80.0 40.0 50.0 60.0 12.0 40.0 50.0 40.0 10.0 40.0 30.0 20.0 40.0 40.0 40.0
4.26000 3.58000 3.29000 2.73000 2.31000 2.06000 1.87000 1.83000 1.82000 1.65000 1.55000 1.54000 1.48000 1.37000 1.32000 1.29000 1.15000 1.11000
20.835 24.851 27.081 32.778 38.958 43.917 48.652 49.787 50.079 55.660 59.599 60.026 62.728 68.425 71.403 73.330 84.107 87.889
13.0 63.0 75.0 100.0 8.0 63.0 15.0 63.0 20.0 31.0 8.0 20.0 8.0 8.0 10.0 13.0 8.0 5.0
Analysis of data from the second stage of research (different dilutions of the post-filtration lye) reveals that for each series of experiments the increasing time of the lye dosage into the DS liquid results in the increase of both bulk and packing densities. Water, oil and dibutyl phthalate absorption capacities decrease with the increasing values of the bulk density for each level of dilution of the post-filtration liquid. The highest values of the bulk and packing densities are found for 3:1 ratio of the lye dilution with water. The bulk density for that series of experiments is in the range 870e1212 g dm3, while the packing density is 1000e1290 g dm3. The physico-chemical properties of calcium carbonate obtained with the use of the diluted DS liquid are analogous to those obtained in other series of experiments. In each series, the elongation of time of the lye dosage into DS results in increasing values of bulk and packing densities and in the decrease of all media absorption capacities. Similar to the effect of the dilution of the post-filtration lye, the use of the diluted DS liquid increases the packing density of the obtained calcium carbonate in comparison to those determined for chalk obtained from the concentrated solutions. The values of the packing density for chalk obtained from the diluted DS liquid are 930e1112 g dm3.
Fig. 2. Particle size distribution and SEM photo of obtained calcium carbonate (post-filtration liquid:H2O 3:1, t ¼ 30 min).
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Fig. 3. Diffraction pattern of calcium carbonate sample with the lowest bulk density.
Analysis of the distribution of the particle size for the obtained calcium carbonate revealed that the crystal size for all samples ranges from 0.316 to 208.930 mm. The size of particles for most samples is in the range 0.316e120.226 mm. The exception is a series in which CaCO3 was precipitated with the diluted post-filtration lye (3:1), with the crystal size in the range 4.365e208.930 mm. That is reflected in the largest values of the crystal diameters calculated for the whole sample volume, as presented in Table 2. Analysis of the distribution of the particle size indicated that the diameter of particles of the obtained CaCO3 decreases with the increasing dilution of the post-filtration lye. The largest particles were obtained with the 3:1 dilution of the lye with water. That results in the largest bulk density. Analogous dependence was found for precipitation of CaCO3 with the diluted DS liquid.
For the selected sample, the distribution of the particle size and the picture from the scanning electron microscopy are presented on Fig. 2. Parameters d(0,1), d(0,5), d(0,9) are the standard values in % and indicate respectively: e d(0,1) particle size [mm] which is larger than the size for 10% of particles in the sample, e d(0,5) particle size [mm] which is larger than the size for 50% of particles in the sample, e d(0,9) particle size [mm] which is larger than the size for 90% of particles in the sample. Parameter d(4,3) indicates the average diameter of the particles as calculated for the whole volume of the sample.
Fig. 4. Example of the EDXRF spectrum for the obtained calcium carbonate.
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The microscopic research revealed that the obtained chalk has a significant tendency to agglomerate. Therefore the dense system of agglomerates of diverse geometrical form was observed and only small amount of single crystals was detected. The qualitative analysis of the precipitated calcium carbonate was performed with the XRD method using the polycrystalline powder samples. The X-ray analyses of the solid phases were based on the distribution curves of the dispersed radiation intensity I ¼ f (q). For each diffraction pattern, the series of interplanar distances (d) and relative intensities (I) were given and compared with data for the respective standards. The characteristic interplanar distances, intensities of the diffracted beams and the Bragg angles for the standards (calcite and vaterite) are presented in Table 3. Fig. 3 presents the typical diffractogram for the sample of precipitated calcium carbonate. Based on the X-ray diffraction (Fig. 3) and the SEM pictures, it was found that calcium carbonate is precipitated in two polymorphic forms e calcite and vaterite. Calcite is the most abundant and very stable polymorphic form of calcium carbonate. Vaterite is the most rare crystal form of CaCO3. It is unstable and undergoes the transformation into calcite. Analysis of the selected samples of calcium carbonate was performed with the scanning electron microscopy. In all investigated samples, most crystals were found in a form of agglomerates of different geometrical form. Samples of chalk with lower bulk density revealed the relatively high amount of single crystals, while in samples of high bulk density a relatively high amount of agglomerates was detected. In the investigated samples, most crystals were of a rhombic shape, characteristic for calcite, as well as the spherical shape corresponding to vaterite. However, the needle form crystals characteristic for aragonite, were not found. The typical SEM picture is presented on Fig. 2. Additionally, to determine the purity of the obtained calcium carbonate, the qualitative analysis of the samples was performed using EDXRF method (Brouwer, 2006). In this method, the sample is irradiated with X-rays emitted by an X-ray tube and the resulting characteristic X-rays generated in the sample (fluorescent X-rays) are detected. By measuring the energies of the radiation emitted by the sample, it is possible to determine what elements are present (qualitative analysis). By measuring the intensities of the emitted energies it is possible to determine how much of each element is present in the sample (quantitative analysis). Analyses were performed with the MiniPal4 PANalytical compact energy dispersive X-ray spectrometer. It was found that the purity of the obtained product is larger than 99%, and the impurities are: Al2O3 (0.28e0.34%), SO3 (0.39e0.54%), Fe2O3 (0.10e0.11%). The example of the obtained EDXRF spectra is presented on Fig. 4. 4. Conclusions CaCO3 from the post-distillation liquid DS and post-filtration liquid from Solvay method of the soda production at 303 K was synthesised. Analysis of data reveals that for each series of experiments the increasing time of the lye dosage into the DS liquid results in the increase of both bulk and packing densities. Absorption capacities for water, oil and dibutyl phthalate decreases with the increasing values of the bulk density. The highest values of the bulk and packing densities are found for 3:1 ratio of the post-filtration liquid dilution with water. CaCO3 obtained for 30 min time of dosage showed the highest bulk
(1212 g dm3) and packing (1290 g dm3) densities. For this sample, the absorption capacities of water, paraffin oil and dibutyl phthalate are the lowest. Formation of agglomerates and only small amount of single crystals was observed. Calcite and vaterite structures of the crystals were evidenced by XRD and SEM.
Acknowledgments The research was financed as the research project MNiSW NN 205 104 135 from the Polish Ministry for Science and Higher Education (2008e2011).
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