Application of amino acids for gold leaching: Effective parameters and the role of amino acid structure

Abstract

The main objective of this research work was to employ different amino acids, and investigate on their capability in gold extraction by leaching process. For this purpose, 8 amino acids (Glycine, Alanine, Valine, Phenyl Alanine, Histidine, Asparagine, Aspartic Acid, and Cysteine) were used to leach native gold and various effective parameters were accordingly verified. The studied parameters were temperature, hydrogen peroxide concentration (as oxidant agent), pH and amino acid concentration. The obtained results indicated that the existence of hydrogen peroxide, moderate temperature, and alkaline pH were the key factors for gold leaching, using amino acids except for Cysteine which could dissolve gold at ambient temperature and in absence of hydrogen peroxide. It was also concluded that the order of amino acids in gold leaching was: Asparagine > Glycine > Histidine > Cysteine > Phenyl Alanine > Valine > Aspartic acid > Alanine. Comparing the leaching rates with related amino acids molecular structures, showed that aliphatic and aromatic amino acids were the lowest effective agents and the existence of N, O, and S donor atoms on the amino acid carbon side chain could be considered as the sign of higher ability for complexing with gold. However, it was also found that the amino acids with just COO− group(s) on the side chain could not dissolve gold effectively. It was also found that all of amino acids are degraded and polymerized during gold dissolution (except Glycine) which leads to spoiling of the agent and has a negative effect on dissolution.