Selective extraction of nickel and cobalt from disseminated sulfide flotation cleaner tailings using alkaline glycine-ammonia leaching solutions

Millions of tons of nickel-bearing tailings, derived from disseminated sulfide resources, has been or are being dumped as waste and the recovery of metals from these tailings is insignificant. There are no economic hydrometallurgical processes to recover valuable metals from such wastes due to their low metal recovery, their alkaline high-magnesium mineralisation, and high reagent requirement. This study presents a novel alkaline process of glycine leaching to extract nickel and cobalt from such tailings. The outcomes of the experimental tests of using an alkaline glycine-based lixiviant system to extract nickel and cobalt from a float tailing material containing 0.79 % Ni and 0.02 % Co respectively are presented in this study. A comparison between using ammonia and sodium hydroxide as pH modifiers was conducted and the leaching performance of glycine -ammonia has been found to be superior based on both metal extractions and leaching kinetics. The use of resin-in-leach (RIL) to recover Ni and Co from glycine-ammonia leaching solution enhanced Ni extraction by -10 %. Grinding of the float tailing sample to a P80 of 15 mu m enhanced both Ni and Co extraction by 10-15 %. Increasing the temperature to 45 degrees C considerably enhanced the metal leaching at which the highest Ni and Co extractions were achieved at 88 % and 90 %, respectively. Controlling dissolved oxygen (DO) levels during the leaching significantly increased the leaching kinetics and decreased the leaching time from 48 to 24 h. QEMSCAN analysis confirmed the selectivity of the alkaline glycine-based system to leach Ni, Co and Cu over impurities such as Fe, Mn and Mg. Two conceptual block diagram flowsheets were proposed for Ni and Co extraction from the float tailings using an alkaline glycine-based leaching process, where the Ni in the original ore is mineralised in an ultramafic, highly disseminated form of pentlandite in a magnesium-rich alkaline gangue matrix.

Automated summary

Traditional hydrometallurgical processes are unable to recover valuable metals from nickel tailings, but the proposed alkaline glycine leaching process can effectively extract nickel and cobalt from the tailings. The experimental results show that alkaline glycine-ammonia system has better leaching performance compared to ammonia alone. Furthermore, the use of resin-in-leach, grinding, increasing temperature, and controlling dissolved oxygen levels can all enhance the leaching efficiency.