Organic constituents of cruds in Cu solvent extraction circuits.: I. Separation and identification of diluent-soluble compounds

Abstract

Interfacial `cruds' from hydrometallurgical solvent extraction of copper ions were examined to assist in the establishment of potential causes of cruds. Diluent-insoluble, polar organics comprised the majority of the solid mass of crud; inorganic particulates and bacterial/fungi were not dominant. Procedures involving ultracentrifugation and acetone extraction were developed to separate these cruds into inorganic, soluble organic, and insoluble organic fractions, and were used to analyze 12 assorted extraction stage and strip stage cruds. UV–Visible and infrared spectroscopic comparisons of the materials with known standard alkarylhydroxyoxime (AAHO) reagents and hydrolysis products were made. Two cruds were further examined by thin layer chromatographic (TLC) separation. Cruds contained larger proportions of de-oximated AAHO than did the supernatant organic phase. Strip stage cruds contained more de-oximated AAHO, relative to the AAHO reagents, than did the respective extraction stage cruds. Cruds contained larger proportions of aliphatic carboxylic acids and aliphatic carboxylic esters, than did the respective supernatant organic solutions. Copper complexes of AAHO reagents were not concentrated in the crud. The polarity of the diluent-insoluble organics was reflected in TLC behavior. Diluent-insoluble organics contained large amounts of carboxylic acids and esters. In experimental trials of the reconstitution of crud from decanted organic and aqueous phases, added diluent-insoluble organics obtained from crud were required for the reconstitution of crud, whereas inorganic particulates were not required. Inorganic particulates were incorporated into the reconstituted crud, but did not reconstitute crud in the absence of diluent-insoluble organics. It was hypothesized that low-polarity, diluent-soluble compounds are less likely to cause crud episodes, or even to be accumulated in crud, than are the diluent-insoluble organics.