Optimisation of the froth flotation process of Chingola refractory ores (cro) by release analysis

Abstract

Release analyses were done on the Chingola Refractory Ores (CRO), which is a mixture of refractory oxides and sulphide copper minerals with an average grade of 1.37% total copper (TCu) with the goal of optimising the froth flotation process of Chingola Refractory Ores. Cupriferous mica, chalcocite, bornite, chalcopyrite, malachite and pseudomalachite were the significant copper minerals in the ore. The influence of mesh of grind of feed, collector and sulphidiser dosages on the flotation of CRO was investigated. The effect of grinding upon the liberation characteristics of the ore was also investigated. Bench scale flotation tests were carried out on samples ground for 2, 4, 8 and 16 minutes. Sodium isopropyl xanthate (SIPX) collector dosages of 30 grams per ton (gpt), 50 gpt and 70 gpt were used. The effect of a sulphidiser, Sodium hydrogen sulphide (NaHS) on the flotation of CRO was also investigated. Bench scale flotation tests were carried out at sulphidiser dosages of 200 gpt and 300 gpt. The liberation of copper in CRO increased with increasing grinding time as evidenced by the decrease in release coefficient ‘a’ and the increase in release coefficient ‘b’ of the modified Hall equation. However, the flotation tests showed that there was an increase in the loss of copper as particle size decreased. Increasing the collector dosage increased the copper recovery. Increasing sulphidiser dosage decreased copper recovery. The best flotation performance was obtained by using SIPX at a dosage of 70 gpt on a sample ground for 2 minutes, where, a concentrate of 15.9% TCu was obtained with 17.8% recovery. Use of sodium hydrogen sulphide resulted in an increase in recovery for the fine sizes. The best results were achieved by using NaHS at 200 gpt, where, a concentrate with 28% TCu was obtained with a recovery of 13.5% from a sample ground for 16 minutes. Low recoveries and concentrate grades were attributed to the unfavourable flotation properties of the cupriferous micas. In addition, the presence of fast floating non-copper bearing micas in the gangue affected the recovery of the floatable copper minerals in the ore. Going by the above findings, it is recommended to incorporate a sulphidisation stage in the flotation process. This would ensure that the process will recover both the copper oxide and sulphide minerals, thus, increasing the total copper obtained in the final concentrate. However, the sulphidisation stage should employ Sodium Sulphide (Na2S.9H2O) as the sulphidising agent. From literature Na2S.9H2O has yielded higher copper recoveries than NaHS. Additionally, it is recommended that flotation experiments be done using alkyl hydroxamates/ chelating reagents as collectors to improve the grade/recovery. The study also highlighted the importance of understanding the ore mineralogy in the development of a flotation procedure since all copper minerals respond differently to different flotation conditions. Further intensive study of the cupriferous mica is recommended to gain a better understanding of the nature of the copper in the mica structure. Keywords: Refractory ores, cupriferous mica, flotation.