| 1. |
- Stenström, Stig, et al.
(författare)
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Extraction of cadmium from phosphoric acid solutions with amines Part I. Extractant selection, stripping, scrubbing and effects of other components
- 1985
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Ingår i: Hydrometallurgy. - 0304-386X. ; 14:2, s. 231-255
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Tidskriftsartikel (refereegranskat)abstract
- Cadmium can be effectively removed from wet-process phosphoric acid (WPA) by solvent extraction using long-chain amines, preferably tertiary amines, as extractants. Stripping can be performed either with water or with acids such as phosphoric or sulphuric acid depending on the final conversion of the cadmium waste. Scrubbing could be necessary in some cases and can be performed with alkali. A factorial design experiment was performed to determine the effects of four different components (H2SO4, HCl, HF, H2SiF6) in WPA on cadmium extraction with Alamine 336. The largest influence on cadmium extraction is seen for the hydrochloric acid, drastically increasing the distribution coefficient. Variations of the concentrations of H3PO4, HCl, HF, Fe and Al were also studied. The extraction of cadmium was seen to be strongly dependent on phosphoric acid concentration. A simple extraction model is proposed indicating that CdCl42− ions are extracted.
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| 2. |
- Stenström, Stig, et al.
(författare)
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Extraction of cadmium from phosphoric acid solutions with amines Part II. Diluent selection, flow-sheet configuration, pilot plant operation
- 1985
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Ingår i: Hydrometallurgy. - 0304-386X. ; 14:2, s. 257-276
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Tidskriftsartikel (refereegranskat)abstract
- A large number of diluents were screened to determine the optimum combination between diluent and extractant. Combinations of a C8 tertiary amine and aromatic diluents or of a C12 tertiary amine and aliphatic diluents do not lead to third-phase formation. A flow-sheet for a solvent-extraction process for treatment of various qualities of wet-process phosphoric acid solutions is proposed. Based on a cadmium purification level of 1 mg/kg, extraction, stripping and scrubbing sections of the process would contain two, two and one stages, respectively. A solvent pre-treatment stage may be necessary in some cases. Co-extraction of acids such as H3PO4, H2SO4, HCI, HF and H2SiF6 can be decreased to very low values by manipulating process variables such as pre-equilibration, phase ratios, diluent and amine concentration. Co-extraction of cations other than cadmium was also investigated. Iron, aluminium and magnesium are not co-extracted while zinc and calcium are co-extracted to some extent. The proposed process can be used either for pollution abatement or in combination with other purification processes to recover some of the valuable cations such as uranium, or to produce more refined phosphoric acid streams.
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| 3. |
- Stenström, Stig
(författare)
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Extraction of cadmium from phosphoric acid solutions with amines. Part III. A thermodynamic extraction model
- 1987
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Ingår i: Hydrometallurgy. - 0304-386X. ; 18:1, s. 1-20
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Tidskriftsartikel (refereegranskat)abstract
- A thermodynamic model for cadmium extraction from phosphoric-hydrochloric acid mixtures has been developed. The model enables calculations of cadmium extraction as well as coextraction of phosphoric and hydrochloric acids to be made. In the aqueous phase Bromley's model for the activity coefficients is adopted. In the organic phase simple expressions for the non-ideal behaviour of phosphoric acid are used. The model is capable of calculating cadmium extraction from 0.02 M up to 6.7 M H3PO4 and chloride concentrations between 0.005 and 0.10 M HCl. For high amine concentrations the prediction for cadmium extraction is too high, indicating that high concentrations of phosphoric acid in the organic phase affect the activity coefficient for the extracted cadmium complex significantly. The thermodynamic constant for the extraction equilibrium has been determined as log K11 = 10.23.
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| 4. |
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| 5. |
- Lindström, E. Börje, et al.
(författare)
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A sequential two-step process using moderately and extremely thermophilic cultures for biooxidation of refractory gold concentrates
- 2003
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Ingår i: Hydrometallurgy. - 0304-386X .- 1879-1158. ; 71:1-2, s. 21-30
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Tidskriftsartikel (refereegranskat)abstract
- In many cases, the use of extreme thermophiles, like the archeon Sulfolobus metallicus, in a continuous bioleaching process of gold concentrates is limited by the arsenic content in the feed. In this work, a sequential two-step bioleaching process for gold-containing refractory pyrite/arsenopyrite concentrates has been investigated for the possibility of lowering the toxicity of arsenic with respect to the extremely thermophilic culture. In the first stage, a moderately thermophilic culture was used followed by the extremely thermophilic S. metallicus in the second stage. It was found that the S. metallicus culture survives higher arsenic concentrations than expected when the concentrate was pre-oxidized at a lower temperature. Thus, with this sequential two-step bioleaching process, it is possible to reduce the toxicity of the released arsenic. Therefore, the use of higher pulp densities of arsenic-containing minerals is enabled. When the leached mineral residues were subjected to cyanidation, cyanide consumption and thiocyanate formation were significantly lower after the second stage. In addition, a somewhat higher gold and silver grade was found in the residue from the concentrate ultimately oxidized by S. metallicus.
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| 6. |
- P.K., Sharma, et al.
(författare)
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Surface characterization of Acidithiobacillus ferrooxidans cells grown under different conditions
- 2003
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Ingår i: Hydrometallurgy. - 0304-386X .- 1879-1158. ; 71:1-2, s. 285-292
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Tidskriftsartikel (refereegranskat)abstract
- The growth characteristics of a strain of Acidithiobacillus ferrooxidans isolated from mine water with ferrous ion, sulfur, or pyrite mineral as sole source of energy have been established. The electrokinetic behaviour of the bacterial cells was investigated and the cell surface groups were characterized by diffuse reflectance FT-IR and FT-Raman spectroscopies. The surface charge on the iron-grown cells (i.e.p., pH 2.0) is different from that on the solid-substrate-grown cells (i.e.p., pH 3.0-3.5) and the surface charge depends on the growth history of the bacteria. The FT-IR and FT-Raman spectra revealed a higher amount of protein content on the surface of the sulfur- and pyrite-grown cells compared to the iron-grown cells. These results suggest that the altered surface charge on the cells is due to differences in the protein content synthesized by bacteria exposed to different growth conditions.
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| 7. |
- Sandström, Åke, et al.
(författare)
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Bioleaching of a complex sulphide ore with moderate thermophilic and extreme thermophilic microorganisms
- 1997
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Ingår i: Hydrometallurgy. - 0304-386X .- 1879-1158. ; 46:1-2, s. 181-190
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Tidskriftsartikel (refereegranskat)abstract
- Biooxidation of a fine-grained, complex zinc and gold-containing sulphide ore has been performed in a series of experiments at bench scale with 201 leaching volume in a series of three continuously stirred reactors. A mixed culture of moderate thermophilic bacteria was used for bioleaching at 45°C and a mixed culture of extreme thermophilic archea were used for bioleaching at 65°C. The leaching yields for zinc were in the range 80-87% with the moderate thermophilic bacteria and 96-98% with the extremely thermophilic microorganisms. It was found that, to obtain a high zinc recovery with a low degree of pyrite oxidation, a fine particle size was essential. Changes in retention time did not influence zinc solubilisation to any greater extent. Due to a high limestone content in the ore, the bioleaching was acid consuming. The acid consumption was strongly dependent on the throughput of ore in the leaching system. Recoveries of gold and silver, of ≈90% and 60-80%, respectively, after cyanidation of the bioleaching residue were obtained, irrespective of experimental conditions.
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| 8. |
- Sidborn, Magnus, et al.
(författare)
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Two-dimensional Dynamic Model of a Copper Sulphide Ore Bed
- 2003
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Ingår i: Hydrometallurgy. - 0304-386X .- 1879-1158. ; 71, s. 67-74
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Tidskriftsartikel (refereegranskat)abstract
- A two-dimensional dynamic model for bioleaching of secondary copper minerals from a pile has been developed. In the model. aeration of the pile is considered to be due to natural convection caused by the density gradient in the air within the bed. The rate of sulphide mineral dissolution is modelled according to the unreacted core model. The transport of ferric ions from the particle surface to the reaction zone is calculated considering film diffusion, diffusion within the particle and reaction kinetics. The rate of oxidation of the ferrous ion by bacteria attached to the ore surface is modelled using the Michaelis-Menten relationship. The influences of temperature, dissolved ferric iron and dissolved oxygen in the leaching solution are considered in the kinetic formulation. The set of partial differential equations is solved using the FEMLAB(R) software. The model was used to study the influence of process variables on copper recovery in the bed with time. This model is a useful tool to aid the design and optimisation of industrial operations.
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| 9. |
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| 10. |
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