Processing of high purity gold from scraps using diethylene glycol di-N-butyl ether (dibutyl carbitol)

An improved process was developed to produce gold with purity > 99.9998% (> 5 N) from gold scraps using dibutyl carbitol (DBC) as an extractant. The extraction of gold into DBC was optimised, which showed that gold could be effectively loaded into DBC up to 190 g/L Au. Only small amounts of other minor elements and impurities, such as Pt, Pd, Ag, Cu and Zn, were extracted into the DBC phase. Fe on the other hand has to be removed by pH adjustment to pH3, prior to solvent extraction. The novel stripping step recovered solid fulminating gold Au2O3×3NH3, which was formed by contacting the gold-loaded DBC with concentrated ammonia. This intermediate product was then further reduced to gold powder by hydrazine. Further washing of this gold powder with nitric acid yielded > 5 N gold.