Study on Extraction Separation of Thioarsenite Acid in Alkaline Solution by CO 3 2 - -Type Tri-n-Octylmethyl-Ammonium Chloride

Abstract

To overcome the problem of arsenic separation and enrichment from an alkaline leaching solution in arsenic-containing dust, a ${\text{CO}}_3^{2-}$ -type tri-n-octylmethyl-ammonium chloride (TOMAC) method for extracting thioarsenite is proposed in this paper. Considering an alkaline leaching solution as the research object, after vulcanization pretreatment, TOMAC transformation and organic phase saturated extraction capacity were measured, and the extraction mechanism was preliminarily studied. First, Cl^--type quaternary ammonium salt was effectively transformed to ${\text{HCO}}_3^{-}$ -type by treating organic phase with saturated NaHCO_3five times. TOMAC was effectively transformed from ${\text{HCO}}_3^{-}$ to ${\text{CO}}_3^{2-}$ type by alkaline washing with 1.0 mol/l NaOH solution; this washing was repeated thrice. Thereafter, the effects of organic phase composition, phase ratio, extraction time, and temperature on the extraction and separation of arsenic were investigated. The results show that under the conditions of 30% ${\text{CO}}_3^{2-}$ -type TOMAC + 15% sec-octanol + 55% sulfonated kerosene, V_O/V_A = 1/1, and 5 min extraction at room temperature, the single-stage extraction rate of As^III is 85.2%. The As^III concentration in raffinate can be reduced to less than 1.33 × 10^-3 mol/l by four-stage countercurrent extraction, and the extraction rate of As^III can exceed 98.4%.

Keywords: CO32--type; alkaline solution; extraction separation; thioarsenite acid; tri-n-octylmethyl-ammonium chloride.