Tracking the Technological Developments and Human Aspects in the Growth of Falconbridge Ltd.

General OverviewFalconbridge started in 1928 as a subsidiary of Ventures Ltd. and a local mining and smelting company in the Sudbury district.  The new company immediately established an vital international link through the acquisition of the nickel refinery in Kristiansand Norway.  Reinforcing the International perspective were the global exploration activities of Ventures and the opportunity of engineering and operating people to participate in the various metallurgical developments associated with the Ventures organization.  The company had through Ventures a call on a strong technical base provided by various research and development organizations including Quebec Metallurgical Industries (QMI); Lakefield Research Ltd.; Falconbridge Metallurgical Laboratory; Research and Development laboratories in Falconbridge (predecessor to the current Falconbridge Technology Centre (FTC) and in Kristiansand Norway.  Quality control laboratories linked to many associated companies such as the Fahralloy Foundry in Orillia, the Industrial Minerals operations at Midland (silica) and Nephton (nepheline syenite); and Falconbridge Dominicana also contributed to this important technical foundation. The interaction of technical and operating people throughout the greater Ventures / Falconbridge Ltd. organization that led to valuable diffusion of knowledge and skills from one site to another and expanded the experience and capabilities of the people involved and contributed to the expansion and growth of the organization and also to the resilience shown in meeting the many environmental and technical challenges encountered along the way.  These notes provide an overview of major process changes that have occurred over the past 75 years and acknowledge some of the many people involved in these changes through leading the operations, developing new processes, designing and commissioning new facilities and providing executive leadership and inspiration to the organization.
 

1928 – 1952

Overview: Falconbridge in 1952 had survived the depression, the temporary loss of the Norwegian refinery during the Second World War, and the reduced demand for metals that occurred with the conversion to a peacetime economy after 1945.  Economic pressures led to an emphasis on frugality including such symbolic gestures as cutting the pencils, supplied to the operators to fill in shift logs, in half.  The cold war and the Korean conflict led to the US General Supply Administration to initiate a strategic materials stockpiling program.  Nickel was one of the metals considered strategic and provided the initial impetus behind the expansion of Falconbridge nickel operations that lasted nearly 25 years.

Mining & Ore Dressing:  Operations over the first 25 years underwent incremental expansion and improvement in operating procedures.  There were few major changes to the process itself.  Mining initially at number 1 shaft and later at No 5 (main mine) made extensive use of square set mining with timber supplied from the Wahnepetei area by the Poupore Mining Company. Sand and gravel from the extensive moraine deposits were used as backfill.  Ore analyzing about 1.5% nickel and 0.8% copper was processed in the ore dressing plant, a complex of crushers, screens, conveyors, bins and magnetic head pulleys.  Tramp lumber and steel was removed ahead of the primary crusher on a picking belt.  Coarsely crushed ore (3 inches) was magnetically cobbed to give a furnace ore of solid pyrrhotite carrying about 3% nickel.  The ‘non-magnetic’ fraction was crushed to about 1.5 inches and again magnetically cobbed to yield a ‘fine ore’ product. The final ‘non-magnetic product was crushed to about 0.75 inches for milling. 

Falconbridge Mill:  The mill feed was ground in Hardinge conical mills in closed circuit with rake and spiral classifiers.  The grinding capacity was later expanded by addition of a rod mill in closed circuit with cyclones.  The ground ore was floated in Denver No 24 flotation machines and essentially all sulphides recovered for smelting.  The concentrate analyzing about 3.5% nickel was filtered for sintering and the tailings analyzing about 0.12% nickel and less than 1% sulphur was pipelined to an impoundment area where peripheral spigotting was used to build stable, permeable containment berms with fines settling around a central decant tower. The effluent was discharged into a local wetland.

Sinter Plant: The sinter plant comprised six Dwight-Lloyd sinter machines.  Fine ore was used as a grate dressing and filter cake blended with sand flux placed in a 4-6 inch layer over the fine ore and ignited with a burner.  The hot sinter discharged into an expanded chute for transfer in small rail cars to the blast furnaces.  Employees commonly used a mask of woolen cloth over their lower face as a protection from dust and gas.  Process gases flowed through a balloon flue where coarse dust settled for recycle with the sulphur dioxide and fine dust laden gases discharged via the Sinter Stack. Exhaust fans provided local ventilation in the working areas.  Working areas were generally under negative pressure and recycling of gases and dust exhausted through the ventilation system was common.

Blast Furnaces: The blast furnaces were constructed of water-cooled iron casings over a refractory hearth. Coke was used as the fuel and had the additional merits of reducing oxides and improving the permeability of the charge.  The coke comprised less than 10% of the furnace charge by weight but due to its high porosity (low bulk density) was volumetrically much more significant.  The main payload charge comprised hot sinter and furnace ore.  The blast furnaces discharged matte and slag combined through a single taphole into a forehearth or settler from which slag was skimmed more or less continuously into a pot for transfer by rail to a slag dump (granulation was practiced for a period but was dropped due to excessive pump wear as the slag pile got higher. 

Converters: Matte was tapped periodically from the settler for transfer by ladle to a converter.  Converters (initially hand punched, later equipped with automatic punchers) were blown to yield a final low iron shipping matte that was cast, crushed, and shipped in whisky barrels to the Norwegian refinery at Kristiansand.  Flux and fine ore coolant were introduced through a Garr gun firing through the axis of the converter while gas and dust traveled trough a balloon flue to join the furnace off gases in an electrostatic precipitator before discharge to atmosphere through the Main Stack. Slag from the converter was reverted molten to the settler while ladle skulls were crushed and fed to the blast furnace.

Hybinette Process: The Norwegian refinery employed the Hybinette process for refining nickel.  This involved crushing and grinding the matte for multi-hearth roasting to convert the nickel and copper sulphide to oxides.  Roaster gases were scrubbed with dimethyl analine solution (DNA) and a liquid sulphur dioxide product produced in the solvent regeneration process.  The copper was then selectively leached in sulphuric acid (return copper electrolyte) for electro-winning while the nickel was reduced to metal with coke in circular electric furnaces and the impure molten nickel metal cast into anodes.  The anodes were placed in bags in electro-refining tanks.  Purified nickel sulphate solution flowed into a cathode compartment where nickel was plated on nickel starting sheets and the partially denuded electrolyte flowed through the anode bag into the anode compartment where the nickel was replenished.   The level in the anode bag was maintained below that in the cathode compartment to avoid contamination of the catholyte.  Solution purification involved precipitation of all solution impurities including iron, arsenic, cobalt, copper, lead and zinc in a complex series of chemical processes with intermediate thickening and filtration. Soda ash, nickelic hydroxide and powdered nickel were all used in the purification process. The circulating load of nickel in solution was high.  The nickel cathodes were of good quality.  The nickel anode slimes were remelted to give a matte that was reprocessed to recover platinum group metals. Iron slimes were discharged with other effluent solutions (mostly sodium chloride) to the sea.

1953-1977

Overview: This was a period of rapid growth in the company and intensive technological development.  New mines started, new concentrators constructed and new processes developed and applied. Emphasis was placed on separating and processing pyrrhotite, increasing smelter capacity and improving working conditions, developing a more efficient refining process, and underground in developing and improving techniques for bulk mining and establishing expertise in laterite nickel mining and processing.   Existing facilities were modified and improved where not superseded with new plants.

Hydraulic Backfill: The year 1953 represents a watershed year in mining. A pilot plant was built close to the number 5 shaft to produce a hydraulic backfill by desliming Falconbridge mill tailings.   The tailings were piped underground though a ventilation raise to an experimental stope and the techniques that were to provide an important foundation for later development of bulk mining techniques was laid.  The pilot plant provided experience with cyclone classifier operation that was subsequently transferred to concentrator operations.
 
Pyrrhotite Separation: The investigation of wet magnetic separation for production of a pyrrhotite concentrate was also started to provide material for piloting various pyrrhotite treatment processes under consideration while upgrading smelter feed to permit more productive use to be made of existing facilities.

Pyrrhotite Processing: Pyrrhotite processing focused initially on selective sulphate roasting with addition of sodium sulphate to promote selective conversion of the nickel mineral pentlandite (comprising about 3% of the pyrrhotite concentrate) to sulphate in a fluid bed furnace fed through air dispersed slurry feed gun located centrally on the roaster roof.  The furnace was operated at about 780*F a temperature at which while nickel sulphates the bulk of the iron remained as hematite.  The hot calcine was quenched in barren solution after partial passage through a fluidized bed cooler.  A counter-current decantation thickener system was used to separate the nickel bearing solution (pregnant liquor) from the iron oxide and the nickel precipitated from solution with iron turnings and elemental sulphide to give a precipitate analyzing about 20% nickel.  A precipitate filter cake was shipped to the smelter and the denuded (barren) solution returned to the quench tank. The initial commercial scale pilot operation was started in 1955? treated about 150 tonnes per day pyrrhotite.  It was expanded by the addition of a second fluid bed furnace in 1957 to 300 tonnes per day capacity.  The plant operated for several years and was in many respects successful.  Considerable test work was done to address the initial weaknesses that showed up in the initial operation and interesting leads developed.  The challenges identified included:

1. The highly corrosive nature of the wet acid reducing off gas when wet (impinger) scrubbers were used and the formation sticky sodium pyrosulphate compound in the flue system that led to rapid build up in the flues and electrostatic precipitator when dry collection was attempted.  
2. The dilution of the process solution from wash liquors necessitating discard of sodium sulphate solution to maintain the water balance in the system.
3. The new availability of high grade (nickel free) magnetite concentrates for iron ore sintering and hematite pellets from many sources that made by-product iron ore from pyrrhotite leaching less attractive.
4. The restriction on sulphur dioxide emissions that necessitated production of a large tonnage of sulphuric acid for a potentially over-supplied market. 

All of these challenges are potentially answerable and a start was made to evaluate the options on a smaller scale.   A partial answer was seen in conducting the bulk of the roasting operation at a higher temperature with a deficiency of air.  This yielded and off gas essentially oxygen (and sulphur trioxide) free gas high in sulphur dioxide and thus easier to transport, clean and efficiently recovery sulphur dioxide, produce sulphuric acid or reduce to elemental sulphur.   This work was subsequently used to develop a very satisfactory technique for partial roasting of nickel copper concentrate (smelter feed) ahead of electric furnace smelting and also extended to the agglomerative roasting of pyrrhotite to yield an essentially sulphur free iron oxide product with an off gas containing very little dust, very little oxygen and a high concentration of sulphur dioxide preeminently suitable for reduction to elemental sulphur.   A plant with three roasters each with capacity for 500 tonnes per day of pyrrhotite was constructed and was complemented by a plant constructed by Allied Chemical to reduce the sulphur dioxide with natural gas to elemental sulphur.  Both roaster and reduction plant ran well but were abandoned after the First Oil Crisis of 1973 when the price of natural gas rose from $0.50 per thousand cubic feet to over $3.00 per thousand cubic feet.  The roaster calcine was ground and pelletized for direct reduction with coal to a metallic iron pellet in a rotary kiln.   Again the process was rendered uneconomic by the oil crisis and a five fold increase in coal prices and this added to technical difficulties with the kiln operation led to abandonment of the process in 1974?   Since that time pyrrhotite separated in the concentrator has been impounded either with tailings or in a separate area. 

Smelter Expansion:  The quantity of concentrate treated by the smelter gradually increased in spite of upgrading due to pyrrhotite separation.  Initially the tonnage of magnetically cobbed ore going directly to the smelter was decreased and eventually eliminated to permit more pyrrhotite production for the new pyrrhotite processes under development.  The feed grade to the mill consequently increased and in spite of the separation of pyrrhotite this provided an additional source of concentrate fro the smelter.  Additionally the start of new mines and concentrators elsewhere in the Sudbury Basin gradually increased the total tonnage of concentrate to be treated.  Several actions were taken to permit higher production through limited facilities:

1. The proportion of pyrrhotite separated in the concentrators was increased further raising the concentrate grade. 
2. A copper concentrate was produced partly in response to the finding and development of high copper orebodies below the main nickel mines and shipped out for custom smelting initially at INCO and subsequently to the Kidd Creek copper smelter reliving the nickel smelter and the refinery of this additional copper burden.
3. A 300 tonnes per day briquetting plant was constructed at Falconbridge adjacent to the smelter and the resulting briquettes used in place of fine magnetic ore for converter cooling.
4. A sixth sinter machine was installed.
5. The sinter plant operation and sintering process was studied intensively and greater attention directed to feed preparation to increase sinter plant throughput.
6. A new larger blast furnace (number 4) was constructed.
7. The air to the blast furnace tuyeres was enriched with oxygen.
8. A new converter aisle was constructed and an additional converter installed.

These efforts bore success and in 1969? the smelter achieved a new production record by exceeding 100 million pound nickel output.

Norway Refinery: The search for a new more efficient and economic refining process was started at Falconbridge with many alternatives investigated initially. This led to the development of the Matte Leach Process employing hydrochloric acid to leach the matte selectively solubilizing the nickel.  The acid nickel chloride solution, after solvent extraction to remove iron and cobalt, was crystallized as nickel chloride hydrate, washed with saturated nickel chloride solution, centrifuged and dried. Two options for further processing were investigated, electro-winning to produce a pure cathode nickel and thermal hydrolysis to make nickel oxide micro pellets and a chlorine off gas that was burnt in hydrogen to regenerate HCL for crystallization and leaching. that were subsequently reduced in a small rotating kiln with hydrogen gas. The HCL matte leach left a copper sulphide residue containing very little nickel.  This residue was sent in the initial commercially sized pilot plant operation to the matte roaster although other options were considered for a small-scale plant. Hydrogen sulphide was generated and initially burnt although it was the eventual intention in a full-scale facility to react the hydrogen sulphide with chlorine gas from an electrowinning circuit. The refinery meanwhile was investigating an alternative process involving the leaching of matte with chlorine to give a neutral nickel chloride solution and a cooper residue.  Although the selectivity of the chlorine leach was not as good as the hydrochloric acid leach the chlorine leach was eventually adopted and the entire refinery converted in stages to this process.  One of the factors in the decision was concern with the possible escape of hydrogen sulphide in a heavily populated area.  While chlorine was also of concern the refinery had prior experience with handling chlorine.  This provided greater confidence in the process developed in Norway. 

1978 – 2003

Overview: The era started off slowly.  The oil crisis had greatly virtually eliminated the growth in the demand for nickel while the capacity for nickel production initiated a decade earlier continued to come on stream leading to a build up in stocks and depressed prices. Faced with fierce international competition drastic measures were taken to reduce costs.  Additionally environmental regulations were demanding process modifications to process mine and mill effluents, to provide financial assurance for closing out operations and to reduce sulphur dioxide and particulate emissions. Environmental management began to play an increasingly important role in company affairs. Major cuts in staff were made, production at marginal mining operation suspended and many interests in many subsidiary and associated companies sold.  Intense focus was placed on incremental improvement of operations and capital and exploration expenditures slashed.  Counter to this trend was the purchase of the Kidd Creek operation.  The one bright feature in all this was the development of a flourishing custom feed business centred on the newly formed Falconbridge International Limited and directed to finding feed materials globally that could be economically processed by the smelter or the refinery. International competition remained strong throughout this period.  The outlook improved sufficiently by the mid 1990’s that the company felt able to move on several new production ventures including the Collahausi copper operation in Chile, the Raglan operation in Ungava and the continuing expansion of the smelter and refinery to accommodate new production and custom feed.  Intensive pilot plant test work on laterite treatment was resumed linked to the New Caledonia Koniambo deposit centred on the newly constructed and impressive Technology Centre at Falconbridge.

Strathcona Concentrator:  The Strathcona concentrator was virtually reconstructed to provide expanded and more efficient operations.  Large cells were installed, and a separate copper circuit constructed making use of column cells to minimize nickel content of the copper concentrate. The plant was reinstrumented and a new central control facility built.

Electric Furnace: A new smelting operation was commissioned guided by information and experience from extensive piloting of both the roaster and the electric furnace operations.   The new electric furnace operation received all concentrate as dense slurry except for the Raglan operation that shipped a fully dried concentrate using pneumatic handling systems.   Concentrate slurry was partially roasted in two fluid bed furnaces and delivered hot calcine and flux through drag conveyors to initially two and with experience and modifications, a single electric furnace for reduction smelting.  The furnace refractory was extensively protected by an elaborate array of water-cooled copper ‘fingers’.  Sulphur dioxide in the roaster off gas was converted to sulphuric acid.   Metallized matte from the furnace was treated in Pierce Smith converters with the converter slag treated in a separate slag cleaning vessel rather than returned to the electric furnace.  A further development was the extension of a converter to provide a primary converting unit blown to oxidize and slag the iron in the metallized matte.  The matte from the oxidation unit at about 10% iron is then transferred to finishing converters to complete iron oxidation.  This procedure combined with the slag-cleaning unit reduces losses of cobalt to the discarded converter slag.

Raglan Operation:  The Raglan operation had a long gestation period. Exploration work was initiated in the 1950’s and an exploration shaft at Donaldson sunk in the 1970’s.  This patience paid dividends provided a base of knowledge and experience that was transformed in the late 1990’s into a successful operation operating under harsh conditions. The Raglan account needs input from those who actually pioneered the operation and such input will be sought.

Collahausi Operation: Falconbridge have been active in Chile for many decades prior to the initiation of the Collahausi operation a link that has presumably been beneficial in experience and local trust. Again others are more qualified to detail the development of Collahausi.

Environmental Performance:  Falconbridge environmental record in recent years is good.  The reduction of air emissions as sulphur and particulates is impressive; effluents are all controlled and treated wherever necessary.  Changes in tailings practice are reducing the loading in effluent streams. Closure plans for all properties are on file and where possible are being incremented on an incremental basis. Management systems have been developed and are in active use to audit operations and encourage improved performance.  A sustainable development policy commits the company to continually seeking ways to improve performance further.  An active program seeking beneficial uses for by-product materials has been in place for some years and is beginning to show benefits.