Almalyk State Technical Institute, Almalyk, Republic of Uzbekistan

Sh. T. Khojiev, Dr. Eng., Acting Associate Prof., Dept. of Metallurgy, e-mail: hojiyevshohruh@yandex.ru
R. E. Toshkodirova, Dr. Eng., Associate Prof., Dept. of Metallurgy, e-mail: zumrad291014@mail.ru
S. A. Kenjayeva, Doctoral Candidate, Assistant Prof., Dept. of Metallurgy, e-mail: yuldashevasevara0@gmail.com

This study investigates the thermodynamic feasibility of selective arsenic removal from iron oxide pigment obtained from biooxidation-derived technogenic solutions produced during the processing of gold-bearing sulfide concentrates at hydrometallurgical plants. The pigment was found to contain 3.29 wt % of arsenic, significantly exceeding environmental safety limits, thereby necessitating purification. A thermodynamic analysis of the interaction between iron and arsenic compounds with sodium sulfide (Na₂S) was performed over the temperature range of 25–120 °C. The calculated Gibbs free energy values indicate that iron compounds (Fe(OH)₃, FeOOH) remain thermodynamically stable in the solid phase, whereas arsenic compounds (As(OH)₃, FeAsO₄, Fe₃(AsO₄)₂) are converted into sulfide and thiometallate forms. The optimal temperature range for selective purification was established at 40–60 °C. The findings provide a solid scientific basis for developing an environmentally safe and low-waste technology for processing biooxidation residues and producing iron oxide pigments with minimal arsenic contamination.

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