Mining Industry in Canada Digs Deep to Meet Demand for Nickel, Copper
The Sudbury Basin in northern Ontario, Canada, has the dual distinction as one of the world’s largest and richest mineral deposits, as well as the second largest known impact crater on Earth. The Sudbury Basin is home to major mining interests, including the Xstrata Nickel’s Sudbury operation with its Strathcona mill and a smelter where mineral concentrate is converted into high-grade matte containing nickel, copper, cobalt, and platinum. The mill has an annual capacity of 3-million tons of ore per year.
Nickel and copper ore in the Sudbury Basin contain large amounts of dirt, clay, and other minerals that need to be removed through processing that occurs at the mill. Typically, the ore is crushed and ground into slurry that is mixed with water and various chemical reagents used to separate the copper or nickel from waste material. At the Strathcona mill, ore from deep shaft mines is processed into two concentrate streams - a nickel concentrate that’s refined at the Sudbury smelter and a copper concentrate that is treated at the Kidd Creek copper smelter and refinery at Timmins in northeastern Ontario.
The Strathcona mill operates four thickener tanks that are designed to allow the thickened slurry to settle at the bottom where rotating rakes pull the solids to an exit point. As the solids settle, the liquid consisting of water and various chemicals overflow into a launder, or trough, to be recycled back to the mill. The thickener tanks, which measure 100-feet across and 30-feet deep, are constructed of carbon steel, which requires a protective lining system to prevent corrosion caused by the chemical-laden slurry.
Earlier this year, the thickener tanks and launders at the Strathcona mill required relining after their protective coating failed. “The failure resulted from poor technical support,” according to Tnemec coating consultant David Walker, who specified the replacement lining for the tanks. “The old coating was a thin-film epoxy, which was presented as a surface-tolerant liner that did not require abrasive blasting. So the surface had been high-pressure water blasted, which was obviously inadequate.”
Each tank and launder was prepared by the coating contractor, Morin Industrial, for relining in accordance with SSPC-SP5/NACE No. 1, White Metal Blast Cleaning. The new lining applied was Series 396 Bridgeport Glass Armor 960, a thick-film, reinforced, modified epoxy that is manufactured and distributed by Tnemec under license from Bridgeport Chemical. The 100 percent solids epoxy is recommended for immersion service where there is frequent contact with a range of chemicals, including acetic acid, hydrochloric acid, sodium hydroxide, and xylene. The coating was applied to the interior surface of three thickener tanks, rake arm mechanisms, and launders, as well as three steel flotation cells. A fourth thickener tank is scheduled for recoating next spring.
On the first thickener tank and launders to be relined, the new lining was applied at 50 to 80 mils dry film thickness (DFT). “The launders were severely pitted,” Walker recalled. “The thickener tank is filled primarily with water, but there is also a very high concentration of chlorides, which is why the steel in these tanks corrode so quickly. They were looking for abrasion resistance, chemical resistance, corrosion protection, and the ability to deal with a severely pitted surface.”
After the lining was applied on the first thickener tank, high-voltage holiday testing was performed to detect pinholes. The fast-curing epoxy liner enabled this required testing within hours of application so the holidays could be repaired. “During holiday testing, the contractor found more holidays than they wanted,” Walker noted. “The launders were so severely pitted that the applicator informed the owner that going forward they needed to apply more lining. As a result, Series 396 was applied on the two remaining launders at 80 to 125 mils.”
Series 61 Tneme-Liner, a cycloaliphatic amine epoxy, was specified for use on the next two thickener tanks in addition to Series 396. “Because these tanks are so large, early sections that were blasted on the first tank started to rust before the lining could be applied,” Walker explained. “So when they moved to the next two tanks, they would blast for a day, stop, clean it up, and apply Series 61 to protect the steel from rusting. Then they would repeat this process on another section until the entire tank was ready to be lined with Series 396.”
In addition to its use at Strathcona mill, Walker observed that Series 396 is used to line slurry tanks at major potash mines in the western province of Saskatchewan. As the top producer of potash in the world, Canada is experiencing an explosion of mining activity that could add more than 17-million tons a year over the next decade to the current supply of 55 million tons produced in Saskatchewan.
With seven sulfuric acid plants in northern Ontario and Quebec, Walker envisions a major opportunity for the Glass Armor linings on acid holding tanks. “This represents a tremendous market for the Glass Armor technology, which does not require post curing,” Walker added. “Competitive liners for sulfuric acid holding tanks require post curing at elevated temperatures for a protracted period of time after they’re applied. So the Glass Armor technology offers a distinct benefit.”