Recovery of nitric acid and gold from gold-bearing aqua regia by tributyl-phosphate

摘要

To develop a process for simultaneous extraction and recovery of nitric acid and gold from gold-bearing aqua regia solutions, solvent extraction study was conducted by using tributyl phosphate (TBP) as the extractant. The extraction behaviors of acid from the pure aqua regia, nitric acid, and hydrochloric acid were investigated with varying concentration of extractant, and the concentration ratio of HNO3 and NCl. The simultaneous recovery of HNO3 and Au with the recycling of HCl from the gold-bearing aqua regia solutions was also examined. Selective stripping was then carried out for co-extracted HNO3 and Au. Equilibrium conditions for HNO3 and Au recovery optimized from the experimental results have been found to be: extraction using 80 vol% TBP at O/A ratio of 1, four contacts of stripping for HNO3 at O/A ratio of 1 using distilled water, and two contacts of stripping for Au at an O/A ratio of 1 using a mixed solution at 1:1 (vol.) ratio of 0.1 M sodium thiosulfate (Na2O2S3) and 0.1 M ammonium hydroxide (NH4OH). It was thus possible to simultaneously recover HNO3 and Au from the gold bearing aqua regia solution through co-extraction and selective stripping of HNO3 and Au leaving HCl in the raffinate for recycling.