Development of Technology of Arsenic Removal from Acidic Waste Solutions in the Form of Arsenic Trisulfide

During the laboratory tests the conditions of arsenic removal from acidic waste solutions of metallurgical enterprise in the form of arsenic trisulfide were determined. The technology based on the reduction of pentavalent arsenic to trivalent state with sodium pyrosulfite solution and following arsenic trisulfide precipitation from acidic solution after treatment with sodium sulfide solution was proposed. The arsenic removal proceeds with mechanical stirring, dosing the calculated amounts of reagents and collecting emissions of hydrogen sulfide. With such treatment, about 95% of arsenic, which was in the initial solution, passes into the precipitate. An enlarged laboratory experiment was carried out and the precipitate with 42.6% of arsenic and 46.9% of sulfur was obtained. The precipitate yield was ∼25.7 kg (dry weight) out of 1 m3 of the initial arsenic containing solution. Keywords: arsenic, arsenic trisulfide, acidic waste solutions, sodium sulfide, sodium pyrosulfite

Elastic, Mechanical, and Phonon Behavior of Orpiment Arsenic Trisulfide under Pressure

Arsenic trisulfide (As2S3) has been found to be an excellent glass former at high temperature and pressure. However, there is still some scarcity for the elastic and phonon behavior of the orpiment phase. By using the Dreiding force field of the geometry optimization computations, we investigated the elastic constants, mechanical moduli, and the phonon dispersion of orpiment As2S3 under the pressure from 0 to 5 GPa. Some results of the elastic parameters of orpiment-As2S3 at 0 GPa are consistent with the experimental data. The phonon dispersions for orpiment As2S3 under pressure are also reasonable with previous calculations.

Recovery of Gallium from Simulated GaAs Waste Etching Solutions by Solvent Extraction

Gallium arsenide is used in semiconductor industries worldwide. Numerous waste etching solutions are produced during the processes of GaAs wafer production. Therefore, a complete and eco-friendly technology should be established to recover gallium as a gallium chloride solution and remove arsenic ion from waste GaAs etching solution. In this study, the gallium trichloride and arsenic trisulfide powders were dissolved in ammonia solutions to prepare the simulated solutions, and the pH value was adjusted to pH 2 by nitric acid. In the extraction step, the GaAs etching solutions were extracted using 0.5 M Cyanex 272 solutions in kerosene at pH 2 and 0.1 O/A ratio for 5 min. The extraction efficiency attained 77.4%, which had an optimal ratio of concentration, and the four steps extraction efficiency attained 99.5%. After extraction, iron sulfate heptahydrates were added into the raffinate, and the arsenic ions were precipitated. The removed rate attained 99.9% when the Fe/As ratio was 10. In the stripping step, the organic phase was stripped with 0.5 M hydrochloric acid at 1 O/A ratio for 3 min, and 97.5% gallium was stripped. Finally, the purity of gallium chloride solution was 99.95% and the gallium was seven times the concentration of the etching solutions.