A technology for gold extraction from tailings resulting from polymetallic ore beneficiation

Abstract

We propose a technology for processing of copper-zinc ore flotation tailings with the purpose of extracting gold using ultra-low (10–30 mg/dm3 ) concentrations of NaCN. The material composition of the starting materials was examined using the methods of inductively coupled plasma, gold assay atomic absorption and X-ray diffraction analysis. The NaCN concentration in solution was determined by titrimetric and photometric methods; pH levels were determined by potentiometric analysis. The laboratory studies established optimal conditions for cyanidation of tailings resulting from flotation beneficiation of copper-zinc ores, which underwent preliminary lime treatment: mass fraction of the 0.071-mm mesh minus – 70.5%; duration – 8 h; NaCN consumption – 0.3 kg/t (at a concentration of 30 mg/dm3 ); L:S =1:1. Under these conditions, the gold extraction rate amounted to 32.0–33.6%. Pre-grinding of flotation tailings to the size of 90% of the 30 mm mesh minus led to an increase in gold extraction of up to 41.5–44.7% at an NaCN consumption of 0.6 kg/t of the same concentration and L:S =1.5:1. The results obtained served as the basis for experimental cyanidation of waste tailings according to two schemes, i.e., using tailings of initial coarseness and pre-ground tailings. A good agreement was achieved between the laboratory and experimental results. At present, the use of pre-ground tailings seems unreasonable economically, due to high costs of NaCN (0.6 kg/t vs 0.3 kg/t) and active chlorine (5.6 kg/t vs 1.2 kg/t). According to pilot tests on a flotation tailing sample weighing 67 t (with an Au content of 1.35 g/t), the gold extraction level was 31.9% at an NaCN consumption rate of 0.135 kg/t. As a result, we propose a technology of gold extraction from flotation tailings of copper-zinc ore based on the application of ultra-low concentrations of NaCN. The expected profit can amount to 1276.74 mln RUB per year, with the economic efficiency of 88% and the payback period of 1.4 years).