Assessing potential hydrogen cyanide exposure from cyanide-contaminated mine tailing management practices in Thailand's gold mining

Abstract

This study assessed the effectiveness of the current cyanide management practice of a large gold mine as a case study of Thailand's cyanide-contaminated mine waste management policy. Most gold mines worldwide use cyanide to extract gold from ore, and various cyanide compounds, including hydrogen cyanide (HCN), are then discharged into a tailing storage facility (TSF). From there, HCN volatizes into the air, and people inhaling HCN can experience chronic, acute, or even fatal effects. Although recently only two gold mines operated in Thailand, many new gold mines are under consideration for future. Unfortunately, no specific government regulations for cyanide-contaminated mine waste management exist besides guidelines from environmental impact assessments prepared by the gold mines themselves. This raises concerns that cyanide volatilization may threaten public health. The current study addresses the need for vital scientific analysis by applying AERMOD modeling to simulate HCN dispersion from the gold mine studied, under 20 scenarios of various pH levels and cyanide concentrations. The results show that the HCN emissions cause acute effects to the public under most scenarios. Chronic effects also occur in scenarios of low pH or high cyanide concentration; however, no simulation showed fatalities. This study determined an acceptable cyanide concentration in TSF that is low enough to theoretically avoid dangerous public exposure. Results show that the mine's recent cyanide discharge limit of 20 mg/l, set by the mine itself, is not safe. To limit dangers from the mine's HCN emissions, cyanide levels in tailings must be carefully calculated and regulated using the HCN dispersion model, being sure to account for pH.