A History of Sherritt – Fifty Years of Pressure Hydrometallurgy at Fort Saskatchewan – by M. E. Chalkley, P. Cordingley, G. Freeman, J. Budac, R. Krentz and H. Scheie (Part 1 of 5)

INTRODUCTION

The Beginning

In July 1927, Sherritt Gordon Mines Limited was incorporated, and named after Carl Sherritt and the Gordon family.  Carl Sherritt was an American citizen who worked as a teamster on the construction of the Hudson’s Bay railroad.  He later became a trapper and prospector and staked copper prospects in the Cold Lake area of Manitoba.  J. Peter Gordon was a civil engineer who also worked on the railroad construction and later became interested in mining developments in the area.

The formation of the company was largely due to the efforts of Eldon Brown, a young mining engineer, with the financial backing of Thayer and Halstead Lindsley and the Gordon family (1).

The Discovery of Nickel at Lynn Lake

In 1941, a Sherritt Gordon prospector named Austin McVeigh sampled an outcrop of sulphide-bearing rock near Lynn Lake that assayed 1.5% nickel and 1.0% copper (2).  It was wartime and Sherritt Gordon could neither afford the men nor the equipment necessary to stake and drill the area.  The discovery was kept secret until after the war.

In the summer of 1945, McVeigh started staking in a six mile square area which covered all of the known magnetic anomalies and McVeigh’s original nickel-copper find.  A diamond drill was flown in but drilling on the strongest magnetic anomalies found only magnetite.  In September, the drill was moved to test several weak magnetic anomalies close to Lynn Lake and by the end of the month, an intersection with good ore grade had been made.

By early 1946, Sherritt Gordon had staked 344 claims in a block approximately 10 miles long and 2 to 3 miles wide, completely hemmed in by outside staking.  Sherritt Gordon had secured all of the nickel deposits.

The drilling program continued through 1946 and in January 1947, a high-grade orebody was discovered, finally establishing the presence of sufficient ore at Lynn Lake to warrant production.  By 1946, Eldon Brown was president and managing director of Sherritt Gordon Mines Limited.  At this time it was determined that the copper mine developed from Carl Sherritt’s original claim at Sherridon, had sufficient reserves for only four more years of production. Eldon Brown decided that the mining and milling plant from Sherridon would be utilized to equip the new mine at Lynn Lake.  The story of how not only the mining equipment but also an entire town, including 258 buildings, was moved 265 km over winter ice and trails (3) is a story of tremendous achievement unto itself.

PRESSURE HYDROMETALLURGY

The Early Years

Diamond drill cores from the Lynn Lake exploration program were subjected to flotation testwork at the mill laboratory at Sherridon.  Preliminary results were favourable.  Samples of the nickel concentrate were sent to Professor Frank Forward at the Department of Mining and Metallurgy at the University of British Columbia (UBC) for a preliminary evaluation.  In the meantime, Eldon Brown approached the major nickel producers, International Nickel and Falconbridge Nickel, with a view to reaching an agreement on custom treatment of the nickel concentrate.  Neither of these companies was prepared to enter into a long-term commitment needed to bring the mine to production.

The only possibility to make the Lynn Lake Project viable was to establish a fully integrated operation to produce concentrate and process it to refined nickel metal.  At that time, conventional nickel technology was to smelt concentrates and produce nickel metal by electrorefining.  The relatively small ore reserves, the remote location and the lack of local supplies of fuel and power made that option unattractive.  These circumstances, and the progress being made at UBC led to the development of pressure hydrometallurgy.  Following a meeting in early 1947 between Eldon Brown and Frank Forward, to discuss possible methods of treating the Lynn Lake nickel concentrate, Eldon Brown stated “We can always smelt and electrolytically refine but if there is a prospect of another method being devised, we should do everything possible to find it.”

Sherritt Gordon provided funds for a laboratory program at UBC.  Initial efforts focused on adapting the Caron Process, used at Nicaro, Cuba, to the treatment of roasted Lynn Lake concentrate to produce nickel oxide.  Results of this work were presented at the CIMM Annual Meeting in Vancouver in April, 1948 (4).  While the flowsheet was shown to be technically feasible, it was unattractive as it did not produce finished metal and offered no financial advantage over smelting and electrolytic refining.

In the course of some of the leaching experiments, it was observed that if certain conditions of temperature, oxygen partial pressure and ammonia concentration were maintained, the nickel, copper and cobalt present in the concentrate, could be dissolved without prior roasting and reduction.  Iron remained as an insoluble hydrated oxide and sulphur was converted into a soluble form.  It was also found that ammonium carbonate could be replaced by ammonia and ammonium sulphate.

The next step of the investigation was to develop simple and inexpensive methods of separating and recovering the metals and ammonium salts from the leach solution.  The flowsheet contemplated at that time involved acidification of the leach solution with sulphuric acid after boiling off the free ammonia to yield a nickel ammonium sulphate, which could be separated by filtration.  The remaining solution would then be heated to decompose “polysulphides” and precipitate copper sulphide.  Finally, ammonium sulphate could be recovered from the barren solution by evaporation.  By the end of 1948, the results of the testwork were sufficiently promising to justify planning and building a small pilot plant.

In December 1948, a meeting was set up between Sherritt Gordon and the Chemical Construction Corporation (Chemico), a subsidiary of American Cyanamid, who were familiar with the design and engineering of hydrometallurgical operations, and who were also conducting research in the hydrometallurgical field.  Of particular interest to Sherritt was the fact that the Chemico engineers had established that nickel could be deposited from ammoniacal solutions as a metal foil or plate on the reaction vessel walls by reduction with hydrogen under pressure.  It was this fortunate turn of events that brought Sherritt Gordon and Chemico together, and the piloting that followed, that gave birth to commercial pressure hydrometallurgy.

Another major milestone in the development process was the hiring of Vladimir Mackiw by Sherritt Gordon in April 1949.  Dr. Mackiw played an instrumental role in the subsequent stages of process development.  The association between Sherritt and Dr. Mackiw was to last for the next 52 years, during which time the more than 40 patents issued under his name made a significant contribution to the development of pressure hydrometallurgy.  His later roles with the Company included Director of Research and Development, Vice President, and subsequently Executive Vice President.

The first pilot plant, with a capacity of 275 kg of nickel concentrate per day, was located at the Bureau of Mines in Ottawa.  In a reciprocal agreement, Chemico designed the pilot plant and provided some technical assistance to the operation while Sherritt Gordon provided engineering staff to participate in further testwork on hydrogen reduction at the Cyanamid Laboratories in Connecticut.  The Ottawa plant operated intermittently over a period of fourteen months and consisted of a co-current leach, filtration, precipitation of nickel ammonium sulphate, and copper sulphide precipitation.  Initially oxygen was used under pressure to oxidize the concentrate, but was later replaced by air with a suitable ammonia recovery unit to scrub the autoclave vent gas.

The major development was the discovery by Mackiw (5) that copper could be removed first from the leach solution as copper sulphide by modifying the leach to a countercurrent system and ensuring that trithionate and thiosulphate ions were present in adequate amounts to allow copper to be precipitated by boiling the solution at atmospheric pressure.  By this method, a solution could be produced from which pure nickel could be recovered, thus simplifying the process by eliminating the sulphuric acid addition and the nickel ammonium sulphate precipitation step.

By the spring of 1950, it was apparent that the process was technically and economically feasible.  However, many aspects of both chemistry and engineering required further examination before a commercial plant could be designed with competence.  The decision was made to expand the pilot plant and a disused foundry in Ottawa was acquired and converted.  A horizontal, mechanically agitated autoclave was installed for the second stage leach, while a vertical autoclave was used in the first stage.  The second pilot plant operated on a semi-continuous basis for three months in early 1951, treating 275 kg/day of nickel concentrate.  The pilot work on the hydrogen reduction of nickel was transferred to Ottawa at this time, and high-pressure batch reduction autoclaves were included in the circuit.  Following completion of the pilot run, it was recommended that individual unit operations should be tested on a larger scale to provide engineering data for scale up purposes.

The next technical challenge was the chemistry of the nickel reduction step.  Chemico had successfully demonstrated a procedure for depositing nickel onto fine seed particles. The challenge was to develop an economic process for the generation of seed.  The Sherritt Gordon team set out to find a method of producing seed by direct reduction from solution.  In the absence of seed, deposition of nickel occurred only on the vessel walls.  The key to success laid in finding a soluble catalyst that would initiate self-nucleation in a nickel-containing solution.  It was found that a solution of the desired composition of nucleation could be produced economically and simply by using second-stage leach liquor to redissolve the small amount of plating from the walls of the reduction autoclave.

The final challenge was to resolve the issue of high sulphur content in the nickel powder.  The high sulphur level was traced to the presence of residual unsaturated sulphur species, such as thiosulphate, polythionates and sulphamate. Treatment of the reduction feed solution at elevated temperature with oxygen resulted in the oxidation of all unsaturated sulphur species, and the hydrolysis of sulphamate to sulphate.

A third pilot plant, incorporating continuous countercurrent leaching, copper removal, and nickel reduction was operated continuously for about five weeks in early 1952.  The design for the refinery was frozen in July 1952, with completion of construction scheduled for December 1953.

Towards the end of 1952, a fourth pilot plant was assembled in Ottawa.  This circuit was a small-scale replica of the commercial plant and was operated with the objective of identifying and overcoming problems likely to be encountered during plant start up.  The pilot plant operated for about five months, processed 120 tonnes of concentrate and produced 10 tonnes of nickel metal.

The selection of Fort Saskatchewan as the plant site was influenced by several important factors, including the availability of an abundant supply of natural gas for making ammonia, access to the North Saskatchewan River for water supply and the Canadian National Railway for transportation, and was within easy reach of a large centre of population in Edmonton.  Construction work began in May 1952 on a section and a quarter east of the town and took about two and a half years.  The ammonia plant was completed in April 1954, the leaching section was completed in May 1954, and the ammonium sulphate plant in July 1954.

For part two, click here: http://bit.ly/2gRTdVo

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