Issue link: http://resourceworld.uberflip.com/i/963504
60 www.resourceworld.com A P R I L / M A Y 2 0 1 8 MININGWORLD McCue pushes the boundaries of chemical precipitation for mine water treatment by Kathrine Moore McCue Engineering, based in Vancouver, BC, specializes in water treatment and works with engineering consultants, industry, and private landowners all across Canada and the US. McCue Engineering recently proved that chemical precipita- tion has a greater range of water treatment capability than previously thought pos- sible when the company successfully removed antimony, chromium and copper using a chemical precipitation program. Chris McCue, AScT, founder of the com- pany in 2000, and Lynda Smithard, P.Eng., co-owner since 2008, spoke to Resource World about their company and their unconventional precipitation program. McCue Engineering was recently hired to complete the preliminary design of a mine water treatment plant (WTP) for a new gold mine project in British Columbia in support of their Environmental Assessment (EA) using a water profile modeled for the future open pit sump water. Smithard said the water profile was complex and the treatment plan included heavy metals removal by chemi- cal precipitation. Smithard explained that, in this case, the EA required the environmental con- sultant to "predict what the treated water quality coming out of the future plant would look like and how that water quality may or may not impact the envi- ronment. So, they hired us to tell them what they could reasonably expect for water quality coming out of the treatment plant targeting the known or anticipated issues at the mine." The company found that they could not provide data pertaining to some of the project's target metal contaminants. Smithard said, "We identified a number of data gaps for those three metals in particu- lar." [antimony, chromium and copper]. McCue went through the available lit- erature going back to 1977 and found no data suggesting chemical precipitation would remove those three metals. "We couldn't offer any confidence that the pro- cess would treat those three parameters." It was not possible, given the data available, to say to what degree the water treatment program would work. The regulators and the project stakeholders, including First Nations, required some assurance – some confidence that the WTP would success- fully treat the mine's water. "So, we had to come up with a chemical program. We gave it a shot and it worked," said McCue. McCue Engineering had the oppor- tunity to try out the water treatment program full scale to treat contaminated water at a site in Vancouver – with success. McCue said, "We had originally gone in there [Port of Vancouver] with a different system." The design, based on predicted water quality, started out fine but the inlet water quality quickly rose above what was predicted and what the treatment system could handle. The contaminated site is on the ocean involving metals and salt water. "We quickly bench tested that water with this chemical program and redesigned the system," said McCue. They redesigned the system to successfully remove metals while allowing the salt water to pass through, since the treated water is discharging in a marine environment. "The chemical program selectively removed heavy metal ions while permit- ting sodium and chloride ions to pass through and be discharged to the marine environment, resulting in a significant cost saving for the property owner and a sig- nificant reduction in carbon footprint by reducing the quantity of waste disposal required," said McCue. Smithard writes, in a paper entitled Synthetic Water Calibration for Water Quality Parameters & Water Treatment Program Validation, "Results from McCue's bench scale tests and the subsequent full scale water treatment plant have con- tributed to the body of knowledge for heavy metals precipitation treatment per- formance for antimony, chromium and copper. Previously, literature indicated that no or negligible removal could be achieved for these parameters using chem- ical precipitation." McCue said, "It is a chemical program and that works with a lot of standard settling and filtration equipment. It is a simple plant that is very typical for a mine site. So what we have done is to find a chemical program that will work with that standard water treatment plant and remove those metals. Where in the past we were looking at reverse osmosis on the back end of that plant, which is costly, produces a waste reject that is expensive to dispose of and is operator intensive." With regards to what type of mining projects this water treatment would be applicable, McCue said, "We always say water is water. The source of the water isn't something we think about; we think about what the water contains and what it needs to contain when it goes out the other side. So, this treatment is applicable to any water that has those contaminants it – so, any kind of mining project." Smithard's paper on the water treatment program goes on to say: This work fills in many data gaps in the theoretical end points for water treat- ment by metals precipitation. It further establishes practical end points, which have been demonstrated to be lower than the theoretical ones. McCue's work has provided valuable data on metals precipi- tation performance that could benefit EA work at other mine sites globally." Filling in gaps in knowledge decreases uncertainty as to what level of water treatment and environmental protection can be achieved. Lowering uncertainty helps with gaining social and regulatory acceptance. Better data also helps advance engineering design work more efficiently. Combined, the work will lower both proj- ect risk and cost." On the topic of how McCue Engineering