Role of the reducing agent in tungsten extraction by chlorination with chlorine from an ore enriched by physical means

Abstract

The effect of three reducing agents (sulphur dioxide, pyrite and carbon) on tungsten extraction from a scheelite-wolframite concentrate with chlorine gas was assessed. A low-grade ore (0.9% w/w WO₃) was collected in the San Martín department, San Luis Province, Argentina, and subsequently enriched by physical means (65.73% w/w WO₃). The minerals identified and their reactivities with chlorine were: scheelite (reactive), wolframite (reactive), pyrite (reactive), quartz (inert) and feldspars (inert). The metal recovered as WO₂Cl₂, with the different reagent combinations, was in increasing order: Cl₂ + N₂ < Cl₂ + SO₂ < pyrite + Cl₂ + N₂ < pyrite +Cl₂ + SO₂ < carbon + Cl₂ + N₂. It was proved that, according to its content, the pyrite initially present in the ore improves chlorination performance. At the same time, the non-volatile reaction products formed - CaCl₂ and/or CaSO₄ - and the manner of removing the nascent (desorbed) oxygen change depending on the reducing agent tested.

Keywords:
sulphur dioxide; pyrite; carbon; scheelite-wolframite concentrate; free energy change.