Repurposing of nickeliferous pyrrhotite from mine tailings as magnetic adsorbent for the recovery of gold from chloride solution

The utilization and repurposing of waste materials from mining and minerals industry as low-cost adsorbents for valuable metals have received significant attention due to increasing drive for waste valorization, environmental protection and sustainable development. This study investigates the ability of magnetic nickeliferous pyrrhotite obtained from nickel sulphide mine tailings in Western Australia as adsorbent for gold (Au) from chloride solution. The influence of different variables, such as pH, contact time, initial Au concentration, and chloride (Cl-) concentrations on Au adsorption were examined. The use of magnetic adsorbents is considered as an emerging technology in the recovery of precious metals from aqueous solutions and offers a number of advantages related to ease of solid-liquid separation. The nickeliferrous pyrrhotite samples, composed of pyrrhotite (Fe(1-x)S, 65%), pentlandite ((Fe,Ni)(9)S-8, 32%) and trace impurities of alumino-silicate minerals (3%), were collected manually using a permanent magnet, and were prepared by crushing and grinding to the desired particle size. Complete Au recovery (100%) was achieved after 15 min of contact time at acidic pH. It was also found that the magnetic adsorbent exhibited high loading capacity as evident by 100% Au recovery achieved even at higher initial Au concentrations and after eight times re-use of loaded particles. High Cl- concentration was observed to have a negative effect on Au uptake. The galvanic interaction between pentlandite and pyrrhotite as the possible mechanism for Au recovery is discussed. Repurposing nickeliferous pyrrhotite from mine wastes as magnetic adsorbent for Au offers a very attractive application for the material.