The flotation of metallic arsenic as a function of pH and pulp potential - A single mineral study

Arsenic is a penalty element in base metal gravity and flotation concentrates and during beneficiation efforts are often made to reduce its level in concentrates destined for smelting. In some Australian tin and tantalum circuits this arsenic can occur as elemental arsenic, lollingite, or arsenopyrite. A great deal is known about the flotation of arsenopyrite, but little is known about the flotation of lollingite and arsenic. This paper is concerned with the flotation of metallic arsenic with ethylxanthate as a function of pulp PH and pulp potential (Eh). A synthetic mixture of arsenic metal and quartz was used in all tests. Arsenic was found to be strongly floating (up to 95% recovery in 8 min flotation with Aerofroth 65 frother and 40 g/t of KEX) over the pH range 5-10. At more alkaline conditions, the recovery dropped off slowly with increasing pH. At pH 6, arsenic was strongly floating over the pulp potential range + 125 mV to +275 mV vs. SHE (Standard Hydrogen Electrode) but exhibited an upper limiting threshold value of about +375 mV vs. SHE. The flotation response dropped off slowly with more reducing conditions below about + 125 mV vs. SHE. Here the flotation kinetics were slow. At PH 10, arsenic was found to be strongly floating in the potential range -300 mV vs. SHE up to about +225 mV vs. SHE. Interestingly, no lower limiting potential in the reducing potential range tested (down to -300 mV vs. SHE) was identified. The rate data indicated fast flotation kinetics at pH 10 at potentials less than about + 225 mV vs. SHE. At pH 6, little genuine flotation of metallic arsenic in the absence of collector was observed and it appears that metallic arsenic does not exhibit any significant natural flotability as do some other metals. Importantly, the results of this study show that metallic arsenic could potentially be readily removed from base metal concentrates by controlled potential flotation over a wide range of PH values by a simple reagent combination. Crown Copyright (c) 2007 Published by Elsevier B.V. All rights reserved.