Extraction and separation of gold(III) from hydrochloric acid solutions using long chain structurally tailored monoamides

• Selective extraction of Au(III) from HCl solutions with sixteen synthesized long chain structurally related monoamides is reported.
• The quantitative extraction of Au(III) is observed at less than 5 min.
• 100% back-extraction of Au(III) from the organic solution is reported.
• The structure of monoamides is an important factor in the Au(III) extraction.
• Inclusive separation of Au(III) from selected platinum group and base metal ions is reported.

A series of long chain symmetrical and unsymmetrical monoamides have been prepared with different substituting groups and their extracting ability for Au(III), selected platinum-group and base metal ions like Pt(IV), Pd(II), Rh(III), Cu(II), Fe(III), and Ni(II) from hydrochloric acid solutions has been studied. The structure reactivity relationship with extraction of Au(III) was investigated. A systematic investigation has been carried out on the extraction of Au(III) using N-methyl-N-butylhexylamide (MBHA), N,N-dihexyloctainamide (DHOA), and N,N-di-hexyl-2-ethylhexainamide (DHEHA), which were chosen for further studies. The quantitative extraction of Au(III) with the investigated monoamides is observed at less than 5 min. Au(III) was strongly extracted by these extractants and the extraction increased with increasing hydrochloric acid concentration. Under similar extraction conditions Pt(IV), Pd(II), Rh(III), Cu(II) and Ni(II) were found poorly extracted. Fe(III) was significant extracted only at high hydrochloric acid concentration ⩾5 M. The dominate extracted species of Au(III) is HAuCl4(amide)2. Effective separation of Au(III) from other investigated elements is possible in the whole range of hydrochloric acid medium used (0.5–7 M), and the quantitative back extraction of Au(III) from the organic phase is obtained by using thiourea- HCl solution