Mineral recovery requires a significant volume of water and as a result, efficient use of water and optimization of water recycling are key to successful operations.
by Clinton Strachan
Since mine sites are located in various climatic regimes – with facilities open to precipitation and evaporation – it is important to design mines and mine facilities to accommodate excess precipitation or arid conditions. At times, an independent review of water management at a mine is worthwhile to determine whether best practices for water conservation are being used, or if water conservation measures can be identified that have not yet been considered.
It is with the goal of improving water management that Hecla Mining Company, one of the largest base and precious metals producers in North America, approached Stantec to conduct a water stewardship review at their six active and inactive mines in North America. Four sites were reviewed in 2017, and the remaining two sites will be reviewed in 2018. While three of the sites are in operation and three of the sites are inactive, all six sites are located in net precipitation environments, where collected excess precipitation requires water treatment and permitted discharge. The specific objective of the stewardship review was to identify where water could be conserved and subsequently reduce the volume and cost of water treatment.
The results of the water stewardship review were compiled by Paul Glader, environmental director at Hecla Mining Company, and Clinton Strachan, a principal geotechnical engineer with Stantec. The results thus far will be presented at the upcoming CIM convention in Vancouver, which runs from May 6-9, 2018. The presentation will be held at 2:50 pm on Monday, May 7 in Room 111, and is titled “A Corporate Wide Approach to Water Stewardship during Operations and Closure”.
The operating mines that were reviewed include the Greens Creek Mine in Alaska, the Casa Berardi Mine in Quebec, and the Lucky Friday Mine in Idaho. The inactive operations are the Grouse Creek Mine in Central Idaho, the Republic Mine site in Washington, and the Star/Morning site in northern Idaho.
At each site, the water stewardship review included the following elements:
1. Reviewing, prior to visiting each site, pertinent documents related to water handling and management.
2. Participating in a site visit to understand site conditions, meet with key personnel involved with water management and treatment, and develop or update the site water balance schematic diagram.
3. Using the information collected, identifying water conservation measures and estimate the volume of water conserved, potential reductions in the cost of water management and/or water treatment.
4. Documenting the results for each site in a report for the company to assess whether certain water conservation measures should be assessed in more detail, and enacted.
These elements are discussed below.
Getting the water balance right
Whether a mine’s water supply is from an aquifer, lake or river, identifying the volume of water needed for project start-up and operation is an important part of developing the mine and about which potential investors should be acutely aware. Many factors play into getting the right balance: the amount of precipitation versus evaporation (i.e. the climate); seasonal differences that affect the amount of available water; how the water will be used in the operation; and other claims (e.g. surrounding community claims) to the water.
At each mine, a water balance tool, coupled with input from multiple disciplines (environmental, mill and process, tailings operations, etc.), was used to identify water conservation measures. In addition to knowledge of where water is going in the operation, where flow is measured and how accurately flow is measured are key components of the water balance.
Opportunities to reduce water treatment
Several strategies can be implemented to reduce the volume of water used at the mine. These include ambient water diversion, process water re-use, managing underground water, and reducing water infiltration into surface facilities.
The best way to reduce treating ambient or natural water is to prevent it coming into contact with mined or processed materials. Can the ambient water be separated so it doesn't come into the affected water system and require treatment before discharge?
Significant water savings can be achieved by recycling process water before treatment and discharge. Other small savings are often found by making adjustments to the water treatment plant e.g. adjusting the process or reagent use.
While conserving water during the operation is important, implementing proper water stewardship at closure often brings long-term benefits. Ideally, operational water stewardship efforts should feed into a plan that minimizes water treatment after closure. During closure, the mine no longer has operating revenue, so optimally a mine should minimize water treatment obligations so they don’t extend years into the future.
Hecla’s water stewardship review identified potential conservation measures that could result in significant savings at the operating facilities. These included routing water in a way that differs from current arrangements, or identifying where significant volumes of water will be encountered with future expansion plans. The greatest potential for water savings was with the process water during operations, which is not surprising considering that is where most of a mine's water is utilized. In addition, the review identified smaller water conservation measures or adjustments in water treatment that are worth additional evaluation.
Many mining companies are seeking ways to improve their water management through stewardship programs like Hecla Mining Company’s program. Clearly, companies recognize that water conservation is an important part of ongoing improvements to mine operations that can result in lower water management and treatment costs.
“A Corporate Wide Approach to Water Stewardship during Operations and Closure” will be presented by Clint Strachan of Stantec during the CIM convention in Vancouver at 2:50 pm on Monday, May 7, 2018 in Room 111.
Content originally published on mining.com.
About the author
Clinton Strachan is a vice president for the mining sector at Stantec. A registered professional engineer with a technical specialty in geotechnical engineering, Clinton has over 37 years of experience with the development, design, permitting, construction, operation, and reclamation of mine facilities.