Three-phase Centrifuge Technology Tackles Copper Crud

The Flottweg Tricanter

When mining copper, there are several possible methods for extracting the metal from the ore. A traditional choice is through solvent extraction (SX). Other metals — platinum, gold, cobalt, nickel, zinc or uranium — also are commonly recovered by SX followed by electrowinning (EW), which involves electro-deposition of metals in solution after leaching. Electro-refining uses a similar process to remove impurities from metals.

Most commercial SX plants suffer from the formation of crud — a solid-

stabilized emulsion that commonly accumulates at the aqueous/organic interface in the settlers of solvent-extraction stages. It is caused by a variety of substances entering the SX circuit, such as wind-blown dust, entrained solids from leaching, impurities in plant solutions, and even insects attracted by the lights in the SX plant. While a thin layer of

crud at the aqueous/organic interface can aid coalescence of fine droplets,

excess crud can interfere with phase separation and severely reduce the efficiency of the settlers.

If allowed to build up in the settlers, crud can begin to move to the next mixing stage. This can rapidly cause a “crud run,” resulting in severely increased entrainment. This in turn causes the contamination of electrolytes with the leach solution and organic phase.

The entrainment of electrolyte into the extraction section of solvent extraction can result in loss of copper to the raffinate (in this case when refining copper). Entrainment of organic in the raffinate will result in increased organic losses. Crud typically has an organic content in excess of 50%. Losses of organic with the crud can cost plants from hundreds of thousands to millions of dollars per year.

Traditional methods used to capture crud in the pregnant liquor produced by leaching also remove the liquor captured in the crud and are tedious and labor-intensive. The industry has a more effective approach: Tricanter technology.