Characterization and solidification of arsenic-rich cyanided tailings

Mining processes generates enormous amounts (millions of tonnes) of waste rock and tailings that has to be handled in an appropriate way to avoid pollution of the surrounding environment. Waste rock is a coarse material which is removed to reach the ore and tailings is a fine grained residual material from the mining process.

Tailings are typically pumped as a slurry from the process and is stored at tailings dams. In gold ores, gold contents is typically in the range of grams per ton. Gold often occures as inclusions in sulphide minerals such as arsenopyrite, pyrrhotite and pyrite. In this cases, cyanide is used to distinctly extract the gold,  but the cyanidation process also increases the solubility of co-occuring minerals.  Tailings from gold mining processes are therefore often chemically reactive due to their inherent content of sulphide minerals such as arsenopyrite, pyrite and pyrrhotite. These minerals could be oxidized in contact with atmospheric oxygen and water. From these reactions sulphate and an acid leachate called acid mine drainage (AMD) with a high content of metals is formed.

Information on the occurrence of arsenic species and iron sulphide minerals in cyanidation tailings is essential for predicting the contaminant release over extended period of time. One way of managing cyanidation tailings is the use of a method called “Cemented paste backfill” (CPB), which is a form of solidification. In CPB, low proportions (3 -7 wt %) of cementitious binders are mixed with tailings to form a saturated, monolithic mass. CPB aims to prevent air intrusion into the tailings and serve as a geotechnical support to underground mine cavities increasing operational benefits for the mining industry. To reduce costs of, amendments such as granulated blast furnace slag (GBFS), biofuel fly ash (BFA) and cement kiln dust (CKD) are used for partial replacement of cement in CPB due to their pozzolanic and alkaline properties. The environmental effect of CPB, in particular effects on sulphide oxidation and release of arsenic has not been subject to extensive research. The aim of my project is therefore, to investigate how the release of arsenic from cyanidation tailings is affected by weathering and a CPB-treatment with various amendments. Speciation of arsenic species is conducted by chemical and mineralogical investigations.

The project is funded by the Ramboll Foundation, SUSMIN -Tools for sustainable gold mining in the EU, Norrbotten Research Council and the Centre of advanced mining and metallurgy (CAMM).

Project meeting: Tools for sustainable gold mining in EU (SUSMIN)

Place: Luleå University of Technology
Time: 21-24 September 2016

The objective of the SUSMIN-project is to increase the transnational cooperation and to support environmentally, socially and economically sustainable gold production within EU to decrease import dependency.

Seminar: Remediation of mine waste deposits

This seminar is intended for researchers, professionals, stakeholders and students in the field of mining, environmental engineering, geochemistry and waste management. The purpose of the seminar is to discuss challenges and possibilities by using residual products in the remediation of mine waste deposits.

Program: Remediation of mine waste deposits