Hatch was commissioned by the Mine Environment Neutral Drainage (MEND) Program to complete a study to identify best available technologies economically achievable (BATEA) to manage and control effluent from metal, diamond, and coal mines in Canada. The objective of the study was to provide reference information for potential forthcoming changes within the Metal Mining Effluent Regulations (MMER) to the types of regulated mining facilities, the list of Schedule 4 parameters, and the authorized limits of Schedule 4 concentrations in effluent discharged to the environment. These potential changes are outlined in the Environment Canada 2012 discussion paper, “10-Year Review of Metal Mining Effluent Regulations”. For metal mining effluent, Environment Canada has proposed the addition of aluminum, iron, selenium, and total ammonia to the list of Schedule 4 substances, and has proposed the reduction of authorized limits for arsenic, copper, cyanide, lead, nickel, and zinc. For diamond mining effluent, which is currently not regulated under MMER, Environment Canada has proposed limits for chloride, phosphorus, ammonia, and total suspended solids (TSS) concentrations in effluent discharged to the environment, as well as limits for pH. For coal mining effluent, which is currently not regulated under MMER, Environment Canada has proposed limits for arsenic, aluminum, iron, manganese, selenium, ammonia, and TSS concentrations in effluent discharged to the environment, as well as limits for pH. Other proposed changes include the addition of a new requirement that effluent be non-acutely lethal to Daphnia magna and changes to Environmental Effects Monitoring requirements.
The study describes the effluent management and treatment technologies and techniques currently employed at metal (base metal, precious metal, uranium, iron ore), diamond and coal mine operations in Canada. The study provides an overview of each (sub)sector’s water management and effluent treatment practices and establishes a model effluent treatment process and treated effluent quality to carry forward for use in BATEA selection.
The study identifies effluent treatment technologies that could be considered best available technologies (BAT) for the Canadian mining sector. The technologies were compiled from treatment technologies currently available on the market, both active and passive, that are applicable to the control of effluent quality for current and proposed MMER parameters. The potential BAT technologies were then screened against a set of criteria: “Can this technique achieve current MMER discharge limits?”, “Has this technique been demonstrated at full scale on mining effluent?”, and “Has this technique been demonstrated under representative climate conditions?”. Technologies that satisfied all three criteria were considered BAT, and carried forward for consideration as BATEA. A technical characterisation is presented for each BAT, which describes contaminant removal mechanisms, removal efficiencies and/or achievable concentrations, major equipment, synergies with other technologies, operational challenges, current application at Canadian operations, and capital and operating costs.
For each (sub)sector, BAT technologies were further screened to identify BAT that could be applied to augment the model effluent treatment system. BAT were screened out from consideration if the technology was already included in the model effluent treatment system flowsheet, or if the technology could not improve effluent quality beyond that typically achieved by the model effluent treatment system. For BAT that passed this screening, order of magnitude equipment, installed, and operating cost estimates were prepared, based on capital and operating cost data from vendors and operations, in-house information, and literature.
BATEA for the augmentation of the model effluent treatment system for each (sub)sector were selected based on a comparative assessment of the costs and benefits of the applicable BAT technologies. BATEA selection was bounded by the strict criteria for BATdescribed above and in the context of a model non-greenfield operation with existing effluent management and treatment systems. BATEA for greenfield operations may be different than that selected for existing model operations. Removal efficiencies and/or achievable effluent concentrations are based on reported operations data, literature values, and/or vendor data and may not be possible for every application. Ultimately, BATEA for any given mining operation is site-specific, as a result of the multitude of geographic and operational factors that influence effluent quality, impact the technical feasibility of treatment technologies, and dictate financial constraints on capital and operating expenditures that can be borne by operations while still maintaining economic viability.
Review of the base metal subsector included a total of 43 operations. The model effluent treatment system for the subsector consists of hydroxide precipitation for metals removal and pond-based settling for bulk TSS removal. Coagulant and flocculant are dosed to facilitate metal precipitate and TSS sedimentation. The pond-based system also enables passive natural degradation of ammonia. The pH of settling pond decant is adjusted with carbon dioxide to meet MMER pH limits and/or un-ionized ammonia/toxicity requirements prior to discharge to the environment. The design and nominal flow rates selected to estimate capital and operating costs for system augmentation for the model treatment system were 2,000 m3/h and 870 m3/h, respectively. BATEA was defined as sulfide precipitation with proprietary polymeric organosulfide chemicals for dissolved metals polishing and the model effluent management and treatment system for total ammonia, bulk metals, and TSS removal.
Review of the precious metal subsector included a total of 40 precious metal operations. The model effluent treatment system for the subsector consists of SO2/air cyanide destruction on tailings and low density sludge lime hydroxide precipitation for bulk metal removal from effluent from tailings, mine, and waste rock areas. The design and nominal flow rates selected to estimate capital and operating costs for system augmentation for the model treatment system were 600 m3/h and 180 m3/h, respectively. BATEA was defined as sulfide precipitation with proprietary polymeric organosulfide chemicals for dissolved metals polishing, active aerobic biological oxidation for total ammonia removal, and the model effluent management and treatment system for cyanide, bulk metals, and TSS removal.
Review of the iron ore subsector included all 6 operating iron ore operations. The model effluent treatment system for the subsector consists of pond-based settling for bulk TSS removal with flocculant dosing to aid settling. The design and nominal flow rates selected to estimate capital and operating costs for system augmentationfor the model treatment system were 7,000 m3/h and 3,900 m3/h, respectively. BATEA was defined as the model effluent management and treatment system for TSS, metals, and total ammonia removal.
Review of the uranium subsector included a total of 12 operations. The model effluent treatment system for the subsector consists of 2 stages: a high pH stage for precipitation of metals that precipitate in basic conditions and a low pH stage for metals and other parameters that precipitate or co-precipitate in acidic conditions. Between and after these pH stages, clarification and filtration are employed to separate precipitates from treated water. The design and nominal flow rates selected to estimate capital and operating costs for system augmentationfor the model treatment system were 500 m3/h and 350 m3/h, respectively. BATEA was defined as active aerobic biological oxidation for total ammonia removal and the model effluent management and treatment system for metals and TSS removal.
Review of the diamond sector included a total of 4 operations. The model effluent treatment system for the sector consists of settling pond(s), clarification, and media filtration for TSS removal. Coagulant is dosed into the clarifier. Prior to discharge to the environment, pH is adjusted using sulfuric acid to meet un-ionized ammonia/toxicity limits. The settling and polishing ponds enable passive natural degradation of ammonia and phosphorus.The design and nominal flow rates selected for the model treatment system were 3,000 m3/h and 2,000 m3/h, respectively. These flow rates were used to estimate capital and operating costs for system augmentation. BATEA was defined as the model effluent management and treatment system for chloride, bulk metals, ammonia, and TSS removal.
Review of the coal sector included a total of 16 operations. In the model effluent treatment system for the sector, bulk TSS is removed via pond-based settling and polishing which may be aided by the addition of flocculant. The settling and polishing pond(s) enable passive natural degradation of ammonia. The design and nominal flow rates selected for the model treatment system were 3,000 m3/h and1,000 m3/h, respectively. BATEA was defined as the model effluent management and treatment system for metals, total ammonia, and TSS removal.
For all (sub)sectors, testwork is recommended to confirm proprietary reagent demand, efficacy, and precipitate settleability, as well as to verify that treated effluent complies with toxicity requirements. It is also advised that treated effluent be discharged rather than recirculated for any purpose such that cycling up of residual chemical concentration is limited. Due to the relatively recent adoption of these reagents and the proprietary nature of their formulations, little is known about the long term stability of residuals and the potential for acid generation and metals remobilization. If residuals are not kept stable through prudent disposal techniques, significant costs associated with residuals stabilization technology or re-treatment of residual leachate could be incurred. Hatch cautions that this technique should only be considered BATEA for operations that are capable of and dedicated to careful control of operating regimes to prevent effluent toxicity, as well as, careful control of residuals storage conditions to prevent long term instability and the potential generation of acid through sulfide oxidation and metals remobilization.
