Distribution of germanium under lead smelting conditions

Abstract

Germanium is present as a minor element in most mined lead-zinc concentrates, and during subsequent processing part of it is carried in electrolyte to zinc electrowinning. Germanium is well known to reduce drastically the current efficiency of zinc deposition and to cause a multitude of pinholes in the cathode deposit, even at concentrations <0·1 ppm, so it is important to understand how to minimise the amount of germanium proceeding to zinc calcines leaching. This work was aimed at determining the distribution of germanium during lead smelting among lead, slag and gas and generating thermodynamic data for use in process modelling. Lead and a small amount of GeO₂ was equilibrated with CaO-SiO₂-FeO-Al₂O₃ slag under oxygen partial pressures from 10^-10 to 10^-12·5 atm at temperatures from 1150 to 1250ºC. It was found that most germanium is incorporated in the slag, some volatilises and little dissolves into the lead. Germanium is present in the slag predominately as GeO and its activity coefficient in this slag is calculated to be in the range 1·44-2·55. The implications of these findings on processing are also discussed.