The objective of the Innovations in Mine Waste Management Program at CANMET Mining and Mineral Sciences Laboratories (MMSL) is to develop technologies or apply existing technologies to reduce the potential environmental liabilities of mine waste in a cost-effective manner. Important program areas include:

• Subaqueous disposal of sulphidic waste rock and tailings;
• Characterization and management of reactive or radioactive waste;
• Lime treatment of sludge, tailings and waste rock;
• Production and characterization of dense stable sludges;
• Case studies and site assessments of long-term prevention and control measures;
• Revegetation and reclamation practices;
• Waste characterization;
• Prevention of acidic drainage;
• Chemical treatment of acidic drainage.

• Abandoned mines;
• Environmental technologies for cold (northern) climates;
• Leaching characteristics of key metals (As, Sb, Se);
• Tailings dam stability;
• Novel prediction methods for acid generation;
• Investigation of alternative disposal methods;
• Total suspended/dissolved solids;
• Microbial characterization for natural processes;
• Transport, fate and impact of emissions;
• Chronic toxicity and metal mixture toxicology.

Waste characterization is the first step in assessing a potential liability and defining environmentally sound waste management practices. In terms of acid generation, proponents must be able to adequately assess the potential for acid generation via chemical and mathematical prediction methods. These predictions form the basis for waste management plans and numerous methodologies are readily available for this purpose. For more information, please contact us.

Prevention of Acidic Drainage

CANMET-MMSL's Environment Group has considerable expertise in prevention of acidic drainage, particularly in the areas of subaqueous disposal, wet barriers and permafrost. Laboratory studies on sub-aqueous tailings disposal have shown oxygen ingress to the tailings interstitial water appears to be limited to the first 10 cm. In addition, secondary barriers consume dissolved oxygen, preventing or significantly reducing oxygen ingress into the mine waste. Additional studies are being completed on the resuspension of tailings and secondary barrier materials under various water-depth and wave-energy scenarios. For more information, please contact us.

Chemical Treatment of Acidic Drainage

At present, the "best available technology economically achievable" (BATEA) for the treatment of acidic drainage is lime neutralization. CANMET-MMSL is investigating ways to improve the lime neutralization process through plant modifications to reduce reagent/operating costs and improve effluent quality. In addition, work is ongoing to further enhance sludge stability and density through novel treatment processes. Field and laboratory studies allow CANMET-MMSL to assess and optimize various aspects related to chemical treatment. For more information, please contact us.

Optimization of Lime Treatment Systems

Several treatment parameters have a significant impact on sludge production and the geochemical stability of the sludge. Through minor modifications to the treatment process, the properties of the sludge generated can be tailored to the plant or site operating priorities.

CANMET-MMSL's Environment Group has studied the effect of various process parameters for their effect on lime consumption, energy requirements, sludge density and stability. The database of field and laboratory information provides a basis to optimize existing treatment operations from the simple on-line systems to more sophisticated High Density Sludge (HDS) processes. Modification in operating parameters can result in considerable cost savings as well as reduction in long term environmental liabilities associated with sludge disposal. For more information, please contact us.

Staged-Neutralization Treatment Technology to Produce Super Dense Sludges

The staged-neutralization process applies crystallization principles to enhance precipitate crystallinity and reduce sludge volume. This process has been patented in the United States and the Canadian patent is pending.

The staged-neutralization process involves neutralizing in a series of steps to control the level of supersaturation during metal precipitation. Preliminary results indicate that in this process chemical overgrowth, not mechanical aggregation, is the primary precipitation mechanism. In laboratory tests, the physical properties of the sludge were greatly improved: densification increased from 25% solids with recycling to 55-67% solids under supersaturation controlled recycling. The settleability of the sludge was extremely fast, 12 m/h, as compared to 4 m/h observed with most sludges. This ability to rapidly dewater allows the sludge to reach its maximum densification much fast than typical sludges. The mean true particle size (not aggregate) triples to 20 micrometres. Unlike most treatment plants in operation, the sludge produced contained crystalline iron compounds rather than an amorphous phase. For more information, please contact us.

Sludge Disposal Options

Despite recent improvements to the traditional neutralization method, it is estimated that as much as 6.7 million cubic metres of lime treatment sludge is produced annually in Canada. In addition, the minerals industry is faced with questions related to the long-term stability of acid mine drainage (AMD) treatment sludges and their environmentally acceptable disposal. Recent studies have indicated that lime sludge is stable, as defined by waste regulations, if disposed of in a pond-type environment. However, the majority of the lime treatment sludge produced is voluminous and consists of an amorphous hydroxyl-carbonate-sulphate-hydrate thatserves to scavenge metal species. Many mine sites choose to dispose of lime sludge with mill tailings to reduce the waste disposal resources required to dispose of tailings and sludge separately. While there is some perception that the addition of lime sludge to a tailings impoundment area may provide buffering capacity, this has yet to be validated. CANMET-MMSL is current investigating various options for sludge disposal to limit metal mobility and to reduce liability and costs associated with sludge disposal. For more information, please contact us.

Mobile Lime Treatment Pilot Plant Facility

CANMET-MMSL's Environmental Group is investigating ways to improve the lime neutralization process for the treatment of acid mine drainage (AMD) and has developed a modular-mobile test facility. The pilot plant configuration consists of a gravity-fed cascade of tanks that utilize stepwise neutralization, aeration, flocculation and sludge recycle processes to produce a high-density sludge and is based on similar industrial plant processes. The treatment facility has a flexible design, allowing it to be reconstructed to simulate and optimize a variety of treatment processes. Presently, the plant is running in HDS mode while plans are under way to use the facility to evaluate the staged-neutralization process. For more information, please contact us.

Last Modified: 2003-10-27		Important Notices

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