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Process Development

Sherritt is a recognized leader in the application of pressure hydrometallurgy and has more than 60 years of experience in the development and commercialization of hydrometallurgical processes for the recovery of metals.  With a long history as an operator of pressure hydrometallurgical circuits, we use our expertise to help clients unlock the value in ores and concentrate feeds. This covers a range of services including:

  • Metallurgical testing
  • Feed materials characterization and evaluation
  • Batch and continuous unit operations testing
  • Integrated pilot plant testing
  • Construction materials evaluation
  • Flowsheet and process design criteria development

A number of commercial plants are currently operating using our proprietary technologies which include the following core processes:

We also work with clients to develop and commercialize processes for the recovery of copper, gallium, indium, lead, molybdenum, silver and vanadium, and for the removal of undesirable elements such as arsenic, cadmium, chromium, iron, manganese, selenium, silicon and tellurium. Recent process development studies have included pressure oxidation of copper concentrates, as well as pressure oxidation of copper-arsenic feeds to recover copper while fixing the arsenic as a stable residue. We are confident we can help your company develop the right process.

High pressure acid leaching of nickel laterite

High pressure acid leaching (HPAL) has been developed by Sherritt for recovery of nickel and cobalt from nickel laterite deposits (1 to 3% Ni). Laterite ore is leached at high temperatures (245 to 260ºC) with sulphuric acid to extract nickel and cobalt into solution. After liquid solid separation and solution purification, nickel and cobalt are precipitated as a mixed sulphide intermediate with H2S gas. This intermediate is then refined to produce pure nickel and cobalt metals, using flowsheets based on either acid or ammoniacal leaching of the mixed sulphides.

Sherritt is a major producer of nickel and cobalt using HPAL technology. The Moa Nickel plant has been in continuous operation since 1960 and has been operated as a joint venture between Sherritt and General Nickel since 1994. Sherritt is also the operator for the Ambatovy Nickel Joint Venture in Madagascar, which began commercial production in 2014.


Sherritt provided support in the development of the following commercial HPAL projects, including the licensing of Sherritt’s HPAL and mixed sulphide refining technology for the Murrin Murrin plant.

  • Coral Bay Nickel Corporation (Philippines)
  • Ramu NiCo Management (MCC) Ltd. (Papua New Guinea)
  • Minara Resources, Murrin Murrin HPAL Plant and Metals Refinery (Australia)

Case Studies

Hydrogen reduction of nickel and cobalt

Hydrogen reduction of nickel and cobalt was developed by the Chemical Construction Company as an alternative to electrowinning for the production of nickel and cobalt metals. [Sherritt obtained the technology, which was subsequently used in the Fort Saskatchewan operation.] High purity nickel and cobalt powders are produced by the following reactions in high pressure autoclaves. Ammonium sulphate is produced as a valuable by-product of this process.

NiSO4 + 2 NH3 + H2 → Ni + (NH4)2SO4

CoSO4 + 2 NH3 + H2 → Co + (NH4)2SO4

This process is highly versatile and has been integrated with acid and ammoniacal leaching flowsheets for the treatment of nickel-copper mattes and for the treatment of mixed nickel-cobalt sulphides from high pressure acid leach (HPAL) operations.


Sherritt’s hydrogen reduction technology has been operating commercially for over 60 years, including at the following plants:

  • Implats, Springs Refinery (South Africa)
  • Norilsk Nickel, Harjavalta Refinery (Finland)
  • BHP Billiton, Kwinana Operations (Australia)
  • Minara Resources, Murrin Murrin HPAL Plant and Metals Refinery (Australia)
  • Sherritt International Corporation, Mixed Sulphide Refinery (AB, Canada)
  • Sherritt International Corporation, Ambatovy Operations (Madagascar)

Case Study

Pressure oxidation of refractory gold ores and concentrates

Many gold ores and concentrates contain fine gold particles locked within sulphide minerals, such as pyrite and/or arsenopyrite, which make this gold unavailable for recovery by conventional cyanide leaching. Sherritt pioneered the use of pressure oxidation technology to treat these refractory sulphide ores and make the gold amenable to recovery by cyanide leaching, including the first commercial application at Homestake’s McLaughlin mine in California in the early 1980s.

Sherritt’s pressure oxidation process has several advantages over other processes used commercially to treat refractory gold feeds:

  • Conversion of iron and arsenic in the feeds to environmentally stable hematite, ferric arsenate and ferric arsenate sulphate solids during the pressure oxidation process;
  • No emissions of SO2 and/or arsenical dusts, or need for equipment to capture SO2 and/or particulates from high temperature gas streams, as required in roasting processes;
  • Ultra fine milling of the ore or concentrate is not required;
  • Faster reaction kinetics and smaller process equipment than bio-oxidation; and
  • High gold recoveries (>95%) possible over a wide range of feed composition (1.5 to 40 wt% S, 0.1 to 20 wt% As) and sulphide mineralogy.


Sherritt’s refractory gold process has been operating commercially for over 30 years, including at the following installations that are currently in operation:

  • Goldcorp, Red Lake Operations (ON, Canada)
  • Barrick/Papua New Guinea, Porgera Joint Venture (Papua New Guinea)
  • Newcrest Mining, Lihir Operations (Papua New Guinea)
  • AngloGold Ashanti, Corrego do Sitio Operations (Minas Gerais, Brazil)

Case Study

Leaching of nickel-copper matte and recovery of platinum group metals

Sherritt’s matte leach process uses sulphuric acid leaching in a combination of atmospheric and/or pressure leaching steps to quantitatively dissolve nickel and copper in nickel-copper matte and produce a high-grade platinum group metal (PGM) concentrate for refining.

Sherritt’s matte leach process has been operating commercially for over 40 years and most of the world’s platinum supply is recovered from matte treated with this process. Sherritt has worked with PGM producers to tailor the process to accommodate differences between plants in matte composition, impurity content, PGM deportment and desired products, including nickel and copper cathodes, nickel powder (hydrogen reduction), crystalline nickel sulphate, and copper sulphides.


The following commercial base metals refineries currently employ Sherritt’s matte leach technology:

  • Implats, Springs Refinery (South Africa)
  • Anglo Platinum, Rustenburg Refinery (South Africa)
  • Northam Platinum Ltd. Refinery (South Africa)
  • Lonmin Refinery (South Africa)
  • Bindura Nickel Corporation, Smelter and Refinery Complex (Zimbabwe – not operating)
  • Stillwater Mining Company Ltd. Refinery (United States)

Pressure leaching of zinc concentrates

Sherritt developed the Sherritt Zinc Pressure Leach Process, in conjunction with Cominco Ltd, as an alternative to conventional zinc roast-leach technology. Direct pressure leaching of zinc concentrate by the following reaction allows zinc to be recovered as zinc solution amenable to conventional purification and electrowinning, while producing elemental sulphur, which can be sold and/or stockpiled, and a solid residue containing impurities, such as iron and silicon.

ZnS + H2SO4 + ½ O2 → ZnSO4 + H2O + So

The process can be readily integrated with existing roast-leach plants or it can be used to replace roasting entirely in a new installation. The advantages of the Sherritt Zinc Pressure Leach Process include:

  • No emissions of SO2 and no need to produce sulphuric acid (H2SO4)
  • Able to treat zinc concentrates with high levels of iron, lead, silica, copper or other impurities and to treat low grade zinc concentrates or bulk concentrates
  • Zinc ferrite, which is formed in roasters and limits zinc recovery in the roast-leach process, is eliminated
  • Lower capital cost and similar operating costs to zinc roast-leach plants
  • Able to integrate with flowsheets that dispose of iron as jarosite, hematite and/or goethite or into flowsheets for the recovery of indium, gallium, germanium, lead or silver

The Sherritt Zinc Pressure Leach Process has been operating commercially for over 30 years. The following installations currently utilize Sherritt’s zinc pressure leaching technology:

  • Teck Resources Ltd, Trail Operations (BC, Canada)
  • Hudbay Minerals, Flin Flon Zinc Refinery (MB, Canada)
  • Shenzhen Zhongjin Lingnan Nonfemet Co. Ltd (Renhua, Guangdong, China)
  • WMC (China)

Case Study

Pressure leaching of copper concentrates

Sherritt has adapted elements of its proven pressure acid leach technology for zinc concentrates, which has been successfully applied commercially in five operating plants, or similarly, adapted elements of high temperature pressure oxidation technology, used in numerous commercial gold operations, in developing viable processes for treating chalcopyrite concentrates. Sherritt has extensively tested medium and high temperature pressure leaching of copper feedstocks in continuous integrated pilot plant operations, from pressure acid leaching through to copper electrowinning. High copper extractions and the production of residues amenable to high recoveries of gold and silver have been demonstrated.

Sherritt’s moderate temperature pressure leach process for chalcopyrite concentrates, largely patterned after its zinc pressure leach process, involves leaching in solvent extraction raffinate or spent electrolyte, under oxygen pressure at 150°C. Small amounts of coal are added as a dispersant to prevent agglomeration of unreacted sulphides with elemental sulphur; this additive is an essential part of the process.

With a fine grind, copper extraction of greater than 98% is readily attainable in a single pass. Alternatively, conditions may be adjusted to limit copper extraction to about 85 to 90% in a first pass leach, followed by recovery of the unleached sulphides by flotation and removal of elemental sulphur, and recycle of the recovered sulphides to the pressure leach; overall copper extraction of greater than 98% is also achievable. The pregnant pressure leach product solution is processed by conventional solvent extraction and electrowinning to produce high-grade copper cathode. Elemental sulphur is separated from the flotation concentrate by melting and filtration. Gold is recovered in high yield, along with a portion of the silver, from the flotation tailings by treatment with lime and conventional cyanidation.

In high temperature pressure leaching of chalcopyrite concentrates, typically carried out at temperatures in excess of 200°C, sulphide sulphur in the concentrate is almost completely oxidized to sulphate sulphur. Oxidation of all sulphides to sulphate means the process is a net sulphate generator and if an acid source is required for a nearby process, e.g., heap leaching of oxide ore, then a savings on neutralization reagent is realized. Clients

  • 1960s Sherritt – Development, treatment of chalcocite and chalcopyrite concentrates
  • 1975 Sherritt-Cominco Copper Process – Development, treatment of pyritic chalcopyrite concentrates
  • 1996 Stillwater Mining Company, USA – Commercial Plant, pressure leach of Ni-Cu matte
  • 1998 Rio Tinto PLC, Spain – Development, pressure leach of copper ore
  • 1998 P.T. Smelting, Indonesia – Commercial Plant, pressure leach of copper anode slimes
  • 1999 HBMS, Canada – Development, pressure leach of copper concentrate
  • 1999 CVRD, Brazil – Development, pressure leach of copper concentrate
  • 2000 KGHM, Poland – Development, leach process for copper-cobalt ore
  • 2001 MK Gold, Spain – Development, pressure leach of copper ore
  • 2002 Anglo Platinum, South Africa – Development, leach process for Ni-Cu-PGM matte
  • 2003 Confidential, South America – Commercial Plant, selective leaching of copper from sulphide concentrate
  • 2005 Companhia Niquel Tocantins, Brazil – Technical Assistance, copper SX and EW
  • 2006 Confidential, South America– Commercial Plant, Phase II - plant expansion, selective leaching of copper from sulphide concentrate
  • 2012 Codelco, Chile – Development, high temperature pressure leach of copper concentrate