Much of Sherritt’s metallurgical and product technology developed over the last 50 years can be traced back to work done during the development of the ammonia leach process. Pressure leaching of sulphide ores and concentrates, using continuous horizontal autoclaves, provided the basis for a thriving pressure hydrometallurgical process licensing business which offered processes for treating nickel mattes and concentrates, zinc concentrates, and refractory gold ores and concentrates.
During the early 1950’s, following the successful commissioning of the nickel refinery at Fort Saskatchewan, Sherritt utilized its laboratory and pilot plant facilities in Ottawa to look for other potential applications for pressure leaching processes in the metals industry. Laboratory tests were carried out on the pressure leaching of uranium ores and on the pressure oxidation of refractory gold ores, where the oxidative pressure treatment proved an excellent method for oxidizing pyrite and arsenopyrite to liberate the gold for subsequent recovery.
Sherritt, under the technical leadership of Vladimir Mackiw, continued to develop acid pressure leaching technology with a series of pilot plant campaigns on a variety of nickel and nickel-copper mattes. Learn More
The acid pressure leach for nickel-cobalt sulphides was licensed to the Finnish nickel company, Outokumpu, in 1967. Two years later the ammonia refining process for nickel concentrates was licensed to Western Mining Corporation in Australia, and a new acid leaching process for separating platinum group metals from nickel and copper sulphides was developed for Impala Platinum in South Africa. By 1991, the latter process has been licensed to five major platinum producers in South Africa. In 1996, the first North American plant, based on the flowsheet at the Western Platinum refinery was commissioned for Stillwater Mining Company in Montana, U.S.A.
More recently in the 1990s, Outokumpu installed hydrogen reduction facilities for nickel production at the Harjavalta refinery in Finland (now owned by Norilsk). Further, Anaconda Nickel (now Minara Resources) in Western Australia adopted the Sherritt pressure acid leach (PAL) process as used at Moa, as well as hydrogen reduction for nickel and cobalt recovery. Learn More
In the 1970s Sherritt’s process research and development resources were spread more widely to include the treatment of both zinc and copper concentrates. The zinc pressure leach process is an environmentally attractive alternative to fluid bed roasting, which produces sulphur dioxide. In the process, zinc sulphide is pressure leached in sulphuric acid solution at 150°C in an oxygen atmosphere to produce zinc sulphate solution and elemental sulphur.
The process was piloted in 1976, and the first commercial plant started up at Trail, B.C. in 1981. The second commercial plant was also in Canada, at the Kidd Creek operation at Timmins, Ontario that was commissioned in 1983. The first overseas plant was built by Ruhr Zink in Germany in 1991. Following that, a third Canadian zinc pressure leach plant was commissioned for Hudson Bay Mining and Smelting at Flin Flon, Manitoba in 1993, the first commercial application of the Sherritt two-stage zinc pressure leach process. Learn More Two subsequent variations of the zinc pressure leach process were commissioned in China at Shenzen Zhongjin Lingnan Nonfemet Co(2009) and Western Mining Co (2015, expected).
A technically and economically viable hydrometallurgical process for the treatment of copper sulphides has long been sought, primarily because of the concern for the environment with regard to sulphur dioxide emissions. Sherritt has developed two potential processes both of which were successfully piloted at Fort Saskatchewan. One is based on ammoniacal pressure oxidation leaching, followed by recovery of the copper from solution as refined copper powder by hydrogen reduction, and produces ammonium sulphate as a byproduct. The other is based on sulphuric acid oxidation leaching and produces elemental sulphur as a byproduct.
Both processes, particularly the latter, are applicable to chalcopyrite, the most abundant and one of the most refractory copper sulphides. In 1971, an intensive and cooperative research program was initiated jointly by Sherritt and Cominco to develop a versatile hydrometallurgical process for producing refined copper and recovering sulphur and other metal concentrates as byproducts from a variety of chalcopyrite containing copper concentrates. After laboratory development of a process that appeared to be economically competitive with smelting, the Government of Canada and the two companies supported the construction, in 1975, and operation, in 1976, of a comprehensive pilot plant facility. The process that resulted from this work is now known as the Sherritt-Cominco (S-C) copper process. More recently, Sherritt has carried out testwork using higher temperature (POX) conditions for treatment of copper concentrates containing varying levels of arsenic. Treatment of these materials at higher temperatures yields a stable residue containing most of the arsenic in the feed (patent pending), which is suitable for impoundment. Learn More
Sherritt’s interest in the pressure oxidation of pyrite containing ores and concentrates was revived in the late 1970s, in the work carried out with Anglo American Corporation of South Africa to develop a process for the pressure leaching of pyrite containing uranium ores. Extensive piloting was carried out and a commercial plant was constructed, but never operated due to a depressed uranium market. Sherritt was engaged from 1977 to 1980, by the Key Lake Mining Corporation, to assist in the development of a process for the very high-grade uranium-nickel-arsenic ores that this company had in northern Saskatchewan. The process that was evolved for this application relied on mild pressure leaching in dilute sulphuric acid in the second stage of a two-stage system. Milling of the ore commenced in October 1983 and full production was achieved, and surpassed, by May 1984. Learn More
Pressure oxidation of refractory gold ores finally came into its own in the 1980s as a healthy gold price encouraged the exploitation of refractory gold ore deposits. Sherritt has played a significant part in the commercialization of pressure oxidation for refractory gold ores. Several pressure oxidation plants have been established since 1985 in the U.S.A. and Brazil. Canada’s first installation, at Campbell Red Lake in Ontario was commissioned in 1991. Two plants were also commissioned in Papua New Guinea, the Porgera operation with startup in 1991 and further expansion in 1994, and the Lihir plant in 1997. More recently, AngloGold Ashanti commissioned a new pressure oxidation facility in 2012 at the site of the original Sao Bento site in Brazil. Learn More
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