Half-charring of dolomite mineral for applications in the passive treatment of mining effluents

Title : Half-charring of dolomite mineral for applications in the passive treatment of mining effluents

Abstract:

The contact between waters and the components of a mine site like open-pit walls, waste rock piles, tailings, access roads, etc., engender effluents contaminated through minerals oxidative dissolution. According to their pH, mine effluents are mainly classified in acidic (acid mine drainage; AMD, pH < 6), circumneutral (contaminated neutral drainage; CND, 6 < pH < 9), basic (pH > 9), diluted, mineralized, or saline. The quality of mine effluents depends on the site mineralogy (the nature and the ratio of acidogenic and neutralizing minerals), climate (rain, snow melt, dryness) and mining operations (open pit / underground mining, chemicals employed). Mine effluents may contain significant concentrations of metals, metalloids, and anions, potentially harmful for humans and environment. Therefore, the treatment of mine effluents is mandatory, and for a mine in operation it can be carried out in water treatment plants. However, hundreds to thousands of years after the mine closure, mine drainage may still impact the environment, its passive treatment being hence the viable option. Passive treatment involves chemical, physical, and biological processes naturally found in the environment, and its set ups (drains, biofilters, wetlands) are preferred for their low cost of construction, operation, and maintenance.

Carbonates rocks as neutralizing minerals are often employed for the passive treatment of AMD. Among carbonates, although less employed than the lime (Ca(CO₃)₂), the dolomite (CaMg(CO₃)₂) is interesting since its reaction with SO₄^2- from the AMD engenders soluble MgSO₄ and therefore reduce the passivation of the carbonate rock by gypsum coating (CaSO₄·2H₂O).

Recently, the half-charring of the dolomite has been studied to produce a new material, CaCO₃·MgO which shows increased reactivity in the AMD / CND treatment. The origins of its improved performance are mainly the formation of MgO by the decomposition of MgCO₃, and the increased surface area of the new material by the release of CO₂. However, the parameters time / temperature in the charring process have to be properly assessed in order to maximize MgCO₃ decomposition without affecting the mechanical strength of the dolomitic stones. The mineralogy and the granulometry (predetermined in passive treatment systems, to preserve the flow properties) also impact the optimum charring conditions of the raw dolomite. In the present study, the half-charred dolomite produced will be employed in passive AMD / CND treatment systems on a closed mine site in Abitibi region of Quebec, Canada.

Audience Take Away Notes:

• The approach to produce half-charred dolomite from raw dolomite, for a specific application: AMD/CND passive treatment in drains, will be presented. Dolomite is a largely available and underused raw material, while half-charred dolomite showed improved efficiency in AMD / CND treatment, stabilization of acidic soil, land restauration, gas adsorption
• Several scientific articles and conference presentations are available in the scientific literature on the subject treated in this presentation (the main author has a few contributions). The research work would be useful for specialists from the mining sector (professionals, students, professors), land reclamation and restauration specialists, forest and agricultural land specialists, environmental professionals
• Definitely, our research is up to date in the mining field
• The dolomite passive treatment system for mine drainage (AMD / CND) consists of the necessary number of modules filled with the mixture of dolomite and half-charred dolomite rocks to obtain treated effluents complying with provincial (Quebec) and federal (Canada) regulations. The modules will be easier to manipulate and replace in comparison to the drains currently employed
• The presentation will provide information concerning the utilization of a new and improved material for the passive treatment of mine drainage (AMD / CND)

Biography:

Dr. Calugaru graduated Mineral Engineering doctoral program of Montreal University (2019). She works as project manager at the Centre Technologique des Residus Industriels (CTRI, Industrial Waste Technology Center) since 2012 and chemistry professor at the College of Abitibi-Temiscamingue since 2008. Dr. Calugaru works in the field of characterization of solids and effluents, physico-chemical and mineralogical modification of materials, passive and active treatment of mine waters, prediction of the quality of the mine drainage, metals recovery by chemical leaching. She has been involved as main researcher or co-researcher in several applied science projects. She has presented her research results in more than 30 scientific articles, conference papers and international conferences.