Abstract
Cyanide (CN−) from gold processing effluents must be removed to protect human health and the environment. Reducing the use of chemical reagents is desirable for small centralized and decentralized facilities. In this work, we aimed to optimize the use of ultraviolet (UV) radiation coupled with hydrogen peroxide (H2O2) to enhance the rate and extent of CN− removal in synthetic and actual gold processing effluents, from one centralized and one decentralized facility in southern Peru. Bench-scale studies conducted using H2O2 and ambient UV showed no significant effects on CN− destruction; however, experiments with higher UV intensity and H2O2 accelerated free CN− degradation. When a 1:1 stoichiometric ratio of CN−:H2O2 was tested, the highly concentrated effluent (1 g CN−/L) had a slower pseudo first-order rate constant (k = 0.0066 min−1) and took ~5 h longer to reach 99% destruction, compared with the low concentration effluent (100 mg CN−/L; k = 0.0306 min−1). Lastly, a TiO2 photocatalyst with low stoichiometric CN−:H2O2 ratios (1:0.1 and 1:0.2), in a compound parabolic solar concentrator, was tested to investigate the degradation of a high concentration effluent (1.28 g CN−/L). These results show a significant improvement to degradation rate within a 20 min period, advancing treatment options for mineral processing facilities.
Highlights
Introduction14.6% of gold production along with the highest share of mining employment
After cyanide reacts with ground ore for approximately 36 h, the water is pumped through granular activated carbon (GAC) supported on a mesh screen with 20 kg of GAC used per m3 of metal/cyanide-containing process water
Effluent from each mineral processing facility was successfully collected from waste
Summary
14.6% of gold production along with the highest share of mining employment. This region produces the third highest output of gold from artisanal and small-scale operations in the country [1]. Growth in gold extraction has brought increased social conflicts, often centering on water supply and, most commonly, water contamination [7,8,9]. This is important in Arequipa, one of Peru’s most arid
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