GOLDSTRIKE TCM PLANT: THERE IS THE FIRST TIME FOR EVERYTHING – Thiosulfate Replacing Cyanide at Goldstrike, NV

"Thiosulfate is infamous in chemistry circles… to contribute to innovation in our industry."

This process became possible only after the Barrick technology team led by Dr. Yeonuk Choi and managed by Dr. Peter Kondos tackled the technology roadblocks identified in the prior to 2000 Barrick thiosulfate developments led by Jacques McMullen. These roadblocks included resin elution, thiosulfate recycling, gold thiosulfate stability and reagent change from ammonium thiosulfate to calcium thiosulfate. The role of Dr. Nathan Stubina and Samir Chefai in resolving some of these roadblocks, as well as the AuTec and CSIRO teams’ tireless work were pivotal to the success of this process development and implementation.

PUEBLO VIEJO MINE AT DOMINICAN REPUBLIC: MAXIMIZING VALUE IN A STATE OF THE ART MINE

Pueblo Viejo is located in the Dominican Republic, approximately 100 kilometers northwest of the capital city of Santo Domingo, and is operated by the Pueblo Viejo Dominicana Corporation—a joint venture between Barrick (60%) and Goldcorp (40%). Development of the project started in 2009, and first production occurred in 2012. The mined ore is processed using conventional methods such as crushing, grinding, pressure oxidation, cyanidation and refining.
Pressure oxidation is done through four autoclaves, each measuring 40m long and 6m diameter. Gold is recovered in CIL (Carbon-in-Leach) by oxidising the ore for about 60 to 75 minutes at 230°C and 3,450 kilo pascals in the autoclaves. This pressure oxidation process was developed at the SGS and AuTec labs under the close supervision of Dr. Yeonuk Choi. An extensive support was also required during start-up, due to challenges with iron and gypsum precipitates formed in the autoclaves.
Two innovations were incorporated into the process design:

•   A hot cure of the slurry from the autoclaves to reduce lime consumption by solid basic ferric sulphate in the CIL circuit, and
•   A lime boil process, involving heating the Counter Current Decantation (CCD) washed slurry to 80°C to 85°C with 35 kg CaO/t to release the silver in the jarosites formed in the Hot Cure Process for improved CIL silver recovery. This is a highly significant innovation, as it provided a valuable silver stream of revenue to the project valued at nearly US$ 1B cash generation, over the life of the project, at the time. This technology increased silver recoveries from 7% to 82%. The Strategic Technology Solutions team under Dr. Peter Kondos and Dr. Yeonuk Choi led this innovation.
• Additional new technology introductions included copper recovery with the formation of copper sulphides with the use of a PAQUES bioreactor.

Additional information can be found in: TECHNICAL REPORT ON THE PUEBLO VIEJO MINE, SANCHEZ RAMIREZ PROVINCE, DOMINICAN REPUBLIC

VOISEY’S BAY NOVEL PROCESS DEVELOPMENT TO RECOVER Ni, Co AND Cu (Vale)

The Long Harbour Nickel (ex-Voisey’s Bay) Processing Plant is a Canadian nickel concentrate processing facility located in Long Harbour, Newfoundland and Labrador.
Operated by Vale Limited, construction on the plant started in April 2009 and operations began in 2014. Construction costs were in excess of CAD $4.25 billion and involved over 3,200 workers generating approximately 3,000 person-years of employment. Operation of the plant requires approximately 475 workers. Production began in July 2014, after it received its first major shipment from its Labrador mine in Voisey's Bay in May 2015. As of that date, a small proportion of the plant's raw materials came from Voisey's Bay but the majority were imported from Indonesia. Voisey’s Bay concentrate is expected to be processed at the Plant by April 2021, when the underground mine at Voisey's Bay will be operational. The plant is designed to produce 50,000 t (49,000 long tons; 55,000 short tons) per year of finished nickel product, together with associated cobalt and copper products.

The nickel industry worldwide has traditionally smelted concentrates produced from nickel, copper and cobalt sulphide ores to make an intermediate sulphide product called matte. Hydrometallurgy has been used for refining the matte to produce high purity nickel, copper and cobalt for the market. Thus, traditional production of these metals has occurred in two steps: smelting and refining. The new hydrometallurgical process that Inco developed processes the nickel concentrate directly to metal products without first having to smelt the concentrate. The concentrate is processed in an autoclave, where it reacts with oxygen and sulphuric acid to produce an impure solution of nickel, cobalt and copper. This solution passes through a number of chemical purification steps (iron removal and solvent extraction stages) ending with removal of impurities and separation of nickel, copper and cobalt. The nickel is recovered by electrolysis as high quality electronickel product suitable for market. The copper and cobalt are recovered as by-products. The waste solids from the process are neutralized with lime and then deposited in a specially designed disposal facility. All water leaving the plant, including precipitation run-off water, is processed to remove contaminants.

Because the hydromet process used at Long Harbour eliminates the requirement for smelting concentrate, it has an economic advantage over the traditional two-step smelting and refining process. The process will also yield more of the valuable cobalt, which is lost to a great extent in the smelting process.