A novel process based on gas filled membrane absorption to recover cyanide in gold mining

Abstract In the last ten years, the operational costs in the gold and silver cyanidation processes have increased, fundamentally, due to the treatment of ores which contains high cyanide soluble metals, such as zinc, copper, and nickel, among others, increasing the cyanide consumption along with the increase in cyanide price. Additionally, the high cyanide consumptions in gold operations have increased the cyanide contents in leach tailings, forcing the inclusion of processes to recover or eliminate cyanide. For these reasons, a membrane contactor operation to recover cyanide from gold mining, using gas filled membrane absorption is proposed in this study, performing laboratory tests in order to determine the throughput of this process and the most relevant parameters, which affect the cyanide recovery. Gas Filled Membrane Absorption (GFMA) process can extract cyanide, using an absorption solution of NaOH. In this process, previously reported for wastewater treatment, a hydrophobic membrane with its pores filled with air separates an aqueous stream containing cyanide and receives a solution with a high pH value. These aqueous solutions cannot penetrate into the membrane pores, promoting the cyanide transfer from the cyanidation solution to the receiving solution. The experimental results show cyanide recoveries higher than 90% in extraction times of approximately 10 min, achieving an average cyanide transfer rate of 0.01 kg m − 2  h − 1 and identifying the pH, feed flow rate and copper concentration as the most influential parameters on the performance of the process. Furthermore, a phenomenological transport model was developed in order to explain the critical steps of the cyanide transfer in the GFMA process. This model was validated by means of the comparison with the experimental results of cyanide extraction with the presence of Cu(I) and Zn(II) ions, obtaining a statistical error lower than 10%. Thus, the gas filled membrane absorption process can recover cyanide, with similar performance to the current cyanide recovery processes, and could involve a smaller size of the equipment due to the high transfer surface area per volume that membrane contactors have.