Continuous Double Recrystallization of Light Soda Ash into Super Dense Soda Ash Harald Oosterhof,* Jan de Graauw, Geert-Jan Witkamp, and Gerda M. van Rosmalen
CRYSTAL GROWTH & DESIGN 2002 VOL. 2, NO. 2 151-157
Laboratory for Process Equipment of Delft University of Technology, Delft, The Netherlands Received November 19, 2001
ABSTRACT: In this work, a new process is explored for the bulk densification of light soda ash. Advantages of the new process are that no (crystal) water needs to be evaporated and that a crystalline super dense soda ash is produced at atmospherical conditions. The so-called “mixed-solvent” process is based on the fact that the transition temperature at which monohydrous and anhydrous soda in contact with an aqueous solution are in equilibrium, can be lowered when a second solvent is applied. Continuous double recrystallization experiments were carried out in mixtures of water and ethylene glycol: first, light soda was recrystallized into monohydrate below the transition temperature, then the temperature was raised above the transition temperature, and monohydrate was converted into solid, anhydrous soda with a high bulk density. Values of up to 1400 kg/m3 were measured. Further, a significant amount of chloride was removed from the soda during the two recrystallization steps. The potential industrial applications of the double recrystallization process are described by Oosterhof et al. (patent application no. EP19980203963 19981124, 2000). Introduction Soda ash from the Solvay process and the monohydrate process (also called the “trona process”) has a low bulk density because the final unit operation in both processes is a calcining step: in the Solvay process sodium bicarbonate (NaHCO3) is calcined:
2NaHCO3 f Na2CO3 + CO2 + H2O
(1)
while in the monohydrate process sodium carbonate monohydrate is calcined:
Na2CO3‚1H2O f Na2CO3 + H2O
(2)
This means that in both processes the solid crystalline intermediate is heated to form a porous end-product because water (and carbon dioxide) is evaporated from the crystal. Both modes of production have a negative influence on the quality of the product: the porous crystals are brittle, which results in breakage during transportation and handling. This causes dusting which is unwanted, especially in the glass industry where the light soda is easily airborne near hot glass furnaces. Another problem that occurs in the glass industry is that the porosity of the light soda gives rise to air bubbles in the final glass product. A final disadvantage of the light soda is its low bulk density. Common values are 550-600 kg/ m3 for the Solvay process and 750-850 kg/m3 for the monohydrate process. Because of this low bulk density, the transport costs are rather high, since for transport by ship not the mass but the volume of the soda determines the costs of transportation. Especially for overseas transportation of soda, which is about 5 Mton/ year from the United States to Europe,1 the volume is the limiting factor. * Present address: Union Umicore Research, Olen Belgium.
Both transport costs and handling problems demand a product with a higher bulk density. Three methods are reported to increase the density: high temperature calcining,2 mechanical compacting,3 and the “monohydration process”. During high temperature calcining, the light soda is heated to temperatures of up to 700 °C for a period of typically 45 min. Under these circumstances, the particles slightly fuse into larger particles with a higher bulk density. During mechanical compaction, light soda ash is precompacted in a screw feeder and then metered to a hydraulic roller press that produces flakes with a density of up to 1800 kg/m3 (the crystal density of Na2CO3 is 2533 kg/m3). Neither Alexanderwerk3 nor Rant4 mentions the bulk density of the final product. The third option which is described by Rant4 is the “monohydration process”: water and light soda are added to a calciner that is operated around 180 °C. At the entrance of the calciner, the temperature of the slurry is approximately 90 °C, and monohydrate is formed. When the temperature increases along the length of the calciner, water is evaporated and dense anhydrous soda is formed. This dense soda has a bulk density of about 1050 kg/m3. The reported energy consumption however is high: 400 kg of steam for each ton of dense soda ash. Notice that each of the processes gives a brittle product: none of the particles is appearing solid or well faceted. Figures 1 and 2 give two scanning electron microscopy (SEM) pictures of both the light soda ash and the dense soda ash from the monohydration process. The difference in particle size and quality is obvious. In this paper, a new method is presented with which light soda ash can be converted into crystalline dense soda ash with a bulk density of up to 1400 kg/m3: the so-called “double recrystallization” process.
10.1021/cg0100336 CCC: $22.00 © 2002 American Chemical Society Published on Web 02/01/2002
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Figure 1. Scanning electron microscopy (SEM) photograph of porous light soda ash (“LSA”) with a bulk density of about 550 kg/m3.
Figure 2. Scanning electron microscopy (SEM) photograph of dense soda ash (“DSA”) with a bulk density of about 1050 kg/m3.
Double Recrystallization Process Sodium carbonate (Na2CO3) is known to have various hydrates of which the anhydrate is stable above 109 °C in aqueous solutions. Below this temperature, mono-, hepta-, and decahydrate can develop, depending on the temperature of the solution. Because a saturated soda solution has an atmospheric boiling point of 105 °C, anhydrate cannot be crystallized during evaporative crystallization at (sub)atmospherical conditions. The influence of ethylene glycol on the transition of monohydrate to anhydrate is described by Oosterhof et al.5 A quantitative relation was established in this work between the concentration ethylene glycol in the mixture and the temperature at which monohydrous and anhydrous soda were in equilibrium. The use of mixtures of water and glycol for the production of dense soda ash is best explained using Figure 3. In this graph, the solubility curves of Na2CO3 and Na2CO3‚1H2O are depicted for a mixture containing 70 wt % glycol (on a salt-free basis). The curves are fitted through experimentally determined solubilities. Above approximately 78 °C, anhydrous soda is stable, below this temperature monohydrate. When (anhydrous) light soda ash is added to the mixture at a temperature below the transition point, it will dissolve until the solution is saturated to monohydrate. Further addition of light soda will then result in a solution that is supersaturated to monohydrate but still undersaturated to anhydrate. As a result, the monohydrate will nucleate and grow, while the anhy-
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Figure 3. Schematical representation of the double recrystallization process using the solubility curves of Na2CO3 and Na2CO3‚1H2O (approximate experimental values in a mixture containing 70 wt % ethylene glycol on a salt-free basis).
drate will further dissolve. The maximum driving force for the crystallization of monohydrate that can be reached is the difference between the solubilities of anhydrate and monohydrate and is given as ∆c1 in Figure 3. The dissolution continues until all light soda ash is converted into monohydrate. The advantage of this recrystallization process is that by precisely adjusting the temperature of the suspension the maximum supersaturation in the solution can be controlled. A subsequent temperature increase to above the transition point creates a driving force for the reverse process: the now unstable monohydrate phase transforms into the stable anhydrate phase. This happens again via a solvent-mediated transition, i.e., monohydrate dissolves while anhydrate nucleates and grows (at a driving force maximally equal to the solubility difference between anhydrate and monohydrate: ∆c2). The recrystallization of soda takes place via the mother liquor. The proposed process has several advantages. First of all, no solvent or crystal water needs to be evaporated, the temperature of the slurry only needs to be altered. The supersaturation (the concentration or chemical potential difference between the stable and unstable phase), the driving forces for both recrystallization steps, can be adjusted by varying the crystallizer temperatures. Finally, the two recrystallization steps can be seen as additional purification steps: the light soda often contains substantial amounts of sodium chloride, especially when the Solvay process is applied. During both recrystallization steps, the unstable phase dissolves and releases sodium chloride and other impurities that are entrapped in the crystal as either inclusion, occlusion, or in the crystal structure. Subsequently, the impurities will be distributed between the mother liquor and the new growing stable phase. This process is repeated twice: first when light soda transforms into monohydrate and again when the monohydrate recrystallizes into dense soda. Both recrystallization steps will therefore contribute to a lower impurity concentration in the crystal product. In a continuous process, where the mixed solvent stream is recycled, an outlet for the impurities has to be created to avoid the build-up of impurities.
Continuous Double Recrystallization of Light Soda Ash Table 1. Summary of the Double Recrystallization Experiments: the Crystallizer Temperatures T1 and T2, the Slurry Residence Time in the Second Crystallizer τ2, and the Weight Percentage Crystals in the Crystallizer, MTa experiment 1 2 3 4 5 6 7 8 9 10 11 12
981116 981123 981201 981216 981218 981223 990122 990209 990212 990309 990315 990316*
T1 (°C)
T2 (°C)
τ2 (min)
MT (wt %)
50 50 50 60 70 60 50 50 50 60 60 60
80 75 90 80 80 80 80 80 80 90 80 80
30 30 30 30 30 30 30 60 15 30 30 60
10 10 10 10 10 20 10 20 20 20 20 20
a A crystallizer with an internal volume of 4.0 L was used for the recrystallization from monohydrate to anhydrate during exp 12 (*).
Crystal Growth & Design, Vol. 2, No. 2, 2002 153 liquor. Subsequently, the samples were placed in a centrifuge to remove the washing liquid. To calculate the degree of conversion (from light soda to monohydrate and from monohydrate to dense soda), the samples were weighed and placed in an oven at 150 °C for at least 24 h. The amount of crystal water in the samples was calculated from the decrease in mass. The concentration chloride in the anhydrous product was determined using a high-resolution ICP-MS (Finnigan Element). Light soda ash was found to contain 0.8 wt % chloride. On the basis of this value, the removal efficiency during the double recrystallization was calculated. Furthermore, the bulk density of the crystal product was determined by weighing the mass of an accurately determined volume of carefully compacted product. Finally, the crystal product was analyzed for its particle size distribution. This was done using a Coulter multisizer II with which the number and volume of the particles can be measured.
Results and Discussion Experimental Section Setup and Chemicals. Several continuous double recrystallization experiments were carried out in a cascade of two crystallizers that are operated as continuously stirred tank reactors (CISTR). Both crystallizers are coated with “Hallar” to prevent scaling. Light soda ash was recrystallized in the first reactor, and monohydrate was recrystallized in the second. Thermostation for the first crystallizer was provided by a Lauda C6 heating bath. The second crystallizer that was always operated at a higher temperature was heated with a more powerful Lauda K6KS. Accuracy of both thermostats was 0.1 °C. Two Lightning (Labmaster SI) stirrers were used for stirring the suspension in both crystallizers. The stirrer speeds were set at 950 rpm which was found to be sufficient to avoid classification (approximate energy input 3 W/kg). The influence of both crystallizer temperatures, the weight percentage solids, and the residence time on the size and quality of the dense soda ash product were investigated; the conversion, bulk density, average particle size, and the purity of the anhydrate crystals were measured. Light soda ash (Akzo Nobel, at least 99% pure) was added to the first crystallizer using a Hethon solids feeder. A Watson Marlow 505DuRL peristaltic pump was used to transport the mother liquor to the first crystallizer. A mixture of water (double-distilled), ethylene glycol (Merck, at least 99% pure), and dissolved soda ash was used for the mother liquor. The composition of the mother liquor mixture was 6 wt % dissolved soda, 0.70 × 94 ) 65.8 wt % glycol, and 28.2 wt % water, which corresponded with a salt-free weight fraction, xEG ) 65.8/(65.8 + 28.2) ) 0.70. Experimental Procedure. At the start of each experiment, both the solids feeder and the peristaltic pump were calibrated to ensure accurate mass flows. Then, both 1.7-L crystallizers were charged with the brine and heated. When both setpoint temperatures were reached, the solids feeder and the pump were started to initiate the experiment. Each experiment was carried out for a period of at least 10 residence times (based on the second crystallizer). A summary of the experiments that were carried out is given in Table 1. The last experiment (12) was carried out using a crystallizer with an effective internal volume of 4.0 L for the recrystallization of monohydrate into anhydrate; in this case, the slurry residence times were 26 and 60 min. In all other experiments, residence time τ1 was approximately equal to τ2, but differed a little due to temperature-dependent densities and the slight change in liquid-phase composition because of the water that was set free during the recrystallization. Slurry samples were taken from both the first and the second crystallizer at approximately 30-min intervals. The size of the samples was about 30 mL. After filtration, acetone was used as a washing medium to remove the adhering mother
The most important experimental conditions and results are given in Table 2. The figures mentioned for the bulk density, average particle diameter (both volume averaged, m4/m3 and number averaged, m1/m0), conversion, and chloride removal are the average of all samples that were taken after 10 residence times. Notice that the stoichiometric amount of crystal water that is determined in the monohydrous samples is always larger than unity, while the anhydrous samples also contain at least a little crystal water in all cases. The hydration numbers mentioned in Table 2 are slightly higher than the theoretical values of 1 and 0, respectively, perhaps due to adhering wash liquid and incomplete conversion into anhydrate. The values of V1 and V2 mentioned in Table 2 can therefore be considered as in general too high. Most valuable information about the final product is therefore gathered by looking at the scanning electron microscopy (SEM) photographs that were recorded. Two typical examples of product from the first and the second crystallizer are given in Figures 4 and 5. On the first, needle-shaped monohydrate is visible, together with some light soda ash that has not been recrystallized yet (middle, right). The other figure shows the product from the second crystallizer: hexagonally shaped anhydrate in various sizes and dissolving monohydrate that can be recognized by its needle-shape with rounded edges. The various types of crystals are well distinguishable as can be seen from those photographs. During the size measurement, however, the Coulter multisizer does not discriminate between the various crystals, which means that the measured values for m4/m3 (the volume based average diameter) and m1/m0 (the number based average diameter) are based on the total sample, i.e., on all particles, both monohydrous and anhydrous. However, when the degree of conversion is high, the few dissolving particles will have a minor contribution to the average size of the final product. Influence of T2. Experiments 1, 2, and 3 (Table 2) show the influence of a change in the temperature of the second crystallizer (T2) on the product. Most obvious, a temperature of 75 °C (experiment 2) is too low to produce anhydrate. In Figure 3, it can be seen that this temperature is indeed below the recrys-
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Table 2. Summary of the Experimental Conditions and Resultsa T1 (°C)
T2 (°C)
τ2 (min)
MT (w%)
Fbulk (kg/m3)
m4/m3 (µm)
m1/m0 (µm)
hydrate number V1
V2
chloride removal (%)
1 3 4 5 6 8 10 11 12
50 50 60 70 60 50 60 60 60
80 90 80 80 80 80 90 80 80
30 30 30 30 30 60 30 30 60
10 10 10 10 20 20 20 20 20
1160 1030 1290 1150 1350 1040 1050 1120 1240
208 142 240 243 212 188 155 162 202
75 73 68 68 86 77 71 67 73
1.11 1.08 1.25 1.15 1.03 1.11 1.23 1.31 1.44
0.66 0.06 0.10 0.15 0.15 0.23 0.59 0.46 0.16
28 42 50 58 56 43 44 53 61
2 7 9
50 50 50
75 80 80
30 30 15
10 10 20
640 980 820
1.08 1.24 1.00
1.26 1.20 0.98
a The nine experiments above the horizontal line yielded anhydrous soda in the second crystallizer, and the three below the line did not. When no (or little) anhydrate was produced, not all analyses were carried out. The hydrate numbers (V1 for the first crystallizer, V2 for the second) is given in mole water per mole anhydrous soda product.
Figure 4. Monohydrate produced with the double-recrystallization process (experiment 5, 70 °C).
Figure 5. Anhydrous soda from experiment 4 with a bulk density of 1290 kg/m3 (T1 ) 60 °C and T2 ) 80 °C).
tallization temperature of about 78 °C. When the temperature is raised to 80 °C in experiment 1, the conversion from monohydrate to anhydrate is increased to 34%, according to the measured water content of the product. From the picture in Figure 6, it can be concluded that the conversion is indeed low: a substantial amount of dissolving needle-shaped monohydrate crystals can be seen in this sample. The average particle size of 208 µm is therefore not reliable since it is strongly influenced by the large percentage of monohydrate in the sample. Duplicate experiment 7 that was carried out to verify these results did not even result in the production of any anhydrate. This lack of conversion is probably because the crystallization is carried out only slightly above the transition temperature, which means that the driving force for conversion was too small:
Figure 6. Influence of the recrystallization temperature in the second crystallizer on the quality of the crystal product. A low conversion is observed at 80 °C and dissolving needleshaped monohydrate can be distinguished.
about 0.05 wt % absolute, corresponding to a maximum theoretical supersaturation of approximately 0.5%. Primary nucleation of the anhydrate is therefore unlikely to occur. Notice furthermore that a small fluctuation in the crystallizer temperature can have a relatively large influence on the prevailing supersaturation, because the recrystallization is carried out close to the transition point. A further increase of the crystallizer temperature to 90 °C results in an almost 100% conversion in experiment 3. This conversion is also confirmed by visual observation: Figure 7 shows a lot of small anhydrous crystals with an average size of about 142 µm. Furthermore, substantial agglomeration can be observed. Experiments 6, 10, and 11 show the same behavior: the highest conversion is obtained at 90 °C (experiment 10), but in this case the difference with the experiments that were carried out at 80 °C (6 and duplicate 11) is much smaller. This might be explained by the higher weight fraction crystals at which these experiments were carried out: 20 instead of 10 wt %. This higher fraction promotes secondary nucleation which means that also at lower driving force a reasonable conversion can be obtained. Influence of T1. Experiments 1, 4, 5, and 7 show that at 50, 60, and 70 °C the conversion of light soda to monohydrate is complete (within the range of inaccuracy). This corresponds with the visual observations of the SEM photographs.
Continuous Double Recrystallization of Light Soda Ash
Figure 7. Influence of the recrystallization temperature in the second crystallizer on the quality of the crystal product. A higher conversion is observed at 90 °C, but the anhydrate particles are rather small.
Crystal Growth & Design, Vol. 2, No. 2, 2002 155
Figure 10. Differential relative volume distributions of monohydrate crystallized at 50, 60, and 70 °C.
Figure 11. Close-up of the product from experiment 4, with the characteristic hexagonal shape of anhydrous soda. Figure 8. Long, needle-shaped monohydrate crystallized at 50 °C.
Figure 9. Long, needle-shaped monohydrate crystallized at 70 °C, having almost the same appearance as the product from a similar experiment that was carried out at 50 °C.
The monohydrous samples that were taken at 50 (experiment 1) and 70 °C (experiment 5) are depicted in Figures 8 and 9. Although it seems that the size distributions look much alike, the Coulter multisizer was used to measure the particle size distribution of the monohydrous product from the experiments 1, 4, and 5. The results are shown in Figure 10: the relative volume of the product is given as a function of the particle diameter. The measured particle size distributions of the various monohydrous products do not differ significantly but the quality of the anhydrous product shows large fluctuations from one experiment to the other, as follows from Table 2. It is interesting to see that the monohy-
drate crystallized at 60 °C has the smallest average particle size. The question now arises: What causes the shape of the solid curve to be different from the other two? An answer is hard to give since quantitative data on the dissolution kinetics of the porous light soda and the nucleation and growth of the monohydrate in mixed solvents are not available. Theoretically, the dissolution rate could either be increased or decreased when the temperature is lowered from 70 to 50 °C: due to the increased concentration difference between the stable and the metastable phase, the dissolution rate is supposed to be higher, but all diffusional processes will take place at a lower rate due to this lower temperature and the higher viscosity it causes. Looking at the final anhydrous product taken from the second crystallizer, the average crystal sizes of the product from experiments 4 and 5 (carried out at 60 and 70 °C) do not differ very much. A slightly higher monohydrate conversion and bulk density are found for experiment 4. Both results might be due to the higher driving force for recrystallization and the larger specific surface area that occur during experiment 4 where T1 ) 60 °C. SEM photographs of the product are shown in Figures 5 and 11. Influence of MT. The weight percentage crystals in the crystallizer directly relates to the yield per volume installed equipment. A higher production rate decreases the investment and capital costs per ton product. For this reason, experiments were performed using mixtures with 25 wt % solids (in the second crystallizer, based on total conversion). However, the experimental setup
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used was found to be inadequate: it was not possible to keep all particles suspended in the (simple) bench scale crystallizer and classification and plugging of the reactor outlet took place. Nevertheless, some indications of the effect of solid concentration can be derived from experiments 4 and 6. With increasing solid concentration, the average particle size of the anhydrate is decreased slightly, which is probably due to secondary nucleation that is dependent on the solids density. Furthermore, the conversion decreases slightly, but the bulk density of the product is increased significantly: to 1350 kg/m3. On the other hand, the duplicate experiment (11) yielded a product with a lower bulk density. Again, this is probably due to the inaccuracy in the crystallizer temperature, resulting in an uncertain value of the supersaturation and thus growth and nucleation kinetics. Higher Conversion. To obtain an even better product quality, several other experiments were carried out. The influence of the residence time τ2 was investigated during experiments 8, 9, and 12. The first two experiments were carried out in the unchanged setup, while during experiment 12, a 4-L second crystallizer was used. A larger crystallizer was used to increase the residence time in the second reactor only (i.e., unchanged residence time in the first crystallizer). The difference between runs 8 and 9, both carried out with a 20 wt % solids content in the crystallizer, is obvious: a larger residence time gives a much larger bulk density and conversion. From the experiments discussed above, it was already clear that the recrystallization of monohydrate to anhydrate takes place rather slowly (see runs 1 and 7: no or hardly any conversion). When the residence time is doubled (experiment 8), the amount of anhydrate produced is increased to 77%, and a decreased residence time of 15 min during experiment 9 does not yield any anhydrate at all. From these results, it can concluded that the recrystallization of the monohydrate into anhydrate occurs at a low rate at 80 °C. To improve the conversion and the product quality, one final experiment (12) was carried out using crystallizer temperatures of 60 (T1) and 80 °C (T2) and residence times of 30 (τ1) and 60 (τ2) minutes. The results of this experiment look very satisfying: a bulk density of 1240 kg/m3 and an average particle size of 202 µm were measured. Chloride Removal. Table 2 also gives the percentage of chloride that was removed from the soda during the experiments. Removal percentages of 28 to 61% were measured. There is a strong correlation between the size and the purity of the product. Notice that the experiments that yielded a product with a large average particle size and a high bulk density (4, 6, 11, and 12) also contain the lowest amount of chloride. From a point of view of kinetics, this is understandable since the lowest impurity uptake is realized when the crystallization of the anhydrous product is carried out under mild conditions (i.e., at a low supersaturation and thus at low nucleation and growth rate). Particles subjected to attrition, however, often have an increased impurity content. A large particle size stimulates attrition. Ap-
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parently, this effect on the purity does not play a dominant role here. Conclusions and Outlook The results of the above-presented exploratory experiments show that it is possible to improve the quality of light soda ash substantially by subjecting it to a double recrystallization step in a mixed solvent. Both the bulk density, the purity, and the average particle size are increased. From the results given in Table 2 and the paragraphs above, the following conclusions can be drawn: (i) The best results were found when the temperature of the first crystallizer was set at 60 °C, while the recrystallization to anhydrate was carried out at 80 °C; a higher value for T2 resulted in the production of small particles with a lower bulk density. Because 80 °C is only slightly above the transition temperature, care should be taken to avoid temperature fluctuations during the crystallization experiments. (ii) A high solids content in the crystallizer does not influence the product properties negatively; the highest bulk density was measured in a mixture containing 20 wt % of anhydrate. (iii) An increased residence time results in a higher conversion, which is quite obvious. (iv) The chloride removal is found to be dependent on the “quality” of the crystallization: if the crystallization is carried out at moderate conditions, the crystal quality improves: both bulk density, conversion, and chloride removal are increased. The operating temperatures of both crystallizers directly limit the maximum supersaturations (∆c1 and ∆c2) at which both recrystallization steps are carried out. Therefore, these temperatures might be optimized with regard to the product quality obtained in these exploratory experiments at xEG ) 0.70. Also, the concentration (and even the type!) of cosolvent might be changed to produce an even better product. To further improve the quality of the soda ash and to increase the level of conversion (which was found to be maximally 85% at 80 °C), the option of increasing the residence time in the second crystallizer should be further investigated. Also, the use of a cascade of crystallizers for the second conversion might be a very promising option. Two or more crystallizers for the production of monohydrate may be desirable too because a full conversion of the light soda is important: any light soda that is transferred to the “hot” stage of the process before it is converted into monohydrate will not be recrystallized anymore, resulting in a decreased quality of the final product. Resuming, it can be stated that the proposed doublerecrystallization technique is a promising alternative for the production of super-dense soda ash: the proposed process can be carried out at atmospheric conditions and only relatively simple equipment is required. The product has an average particle diameter of over 200 µm and a bulk density of more than 1350 kg/m3. Furthermore, a substantial part of the chloride present in the light soda feed is removed during the two recrystallization steps.
Continuous Double Recrystallization of Light Soda Ash
References (1) Thomas, R. Int. Bulk J., 1999, 1, 51. (2) Garrett, D. E. In Natural Soda Ash - Occurrences, Processing and Use; Van Nostrand Reinhold: New York, 1992. (3) Alexanderwerk A. G.; Remscheid; http://www.alexanderwerk.com/dens2•en.html
Crystal Growth & Design, Vol. 2, No. 2, 2002 157 (4) Rant, Z. In Die Erzeugung von Soda nach dem Solvayverfahren; eine verfahrenstechnische darstellung; Enke, Stuttgart, 1968. (5) Oosterhof, H.; Witkamp, G. J.; Van Rosmalen, G. M. AIChE J. 2001, 47, 602-608.
CG0100336
