Reference product: steam, in chemical industry [kg]
Location: GLO - Global
This dataset represents the joint smelting and refining of 1 kg of nickel, 99.5% and 0.243 kg of copper, the former being the reference product. Rough estimate extrapolated from Nickel, 99.5%, at plant dataset (ecoinvent v2.2), representing a global technology of 1994. This dataset is created only to complete Mining and benefication of nickel ore, QC dataset in order to provide a useful product (nickel). The amount of copper refined is calculated based on concentrate caracterisation (see dataset Mining and benefication of nickel ore, QC/GLO). Concerning the other metals in the concentrate (Co, AU, AG, Pt, Pd, Rh; see mining and benefication of nickel ore, QC dataset), since the dataset used for the extrapolation only produced Ni and Cu, no information are avalaible at that time to estimate the inputs associated with the refining of other metals.
[This dataset has been generated using the system model “Allocation at the point of substitution" (APOS). A system model describes how activity datasets are linked to form product systems. The APOS model subdivides multi-output activities by physical properties, economic, mass or other properties allocation. By-products of treatment processes are considered to be part of the waste-producing system and are allocated together. Markets in this model include all activities in proportion to their current production volume.
Version 3 of the ecoinvent database offers three system models to choose from. For more information, please visit: https://www.ecoinvent.org/database/system-models-in-ecoinvent-3/system-models-in-ecoinvent-3.html)]
Extrapolated from a typical technology for smelting and refining of nickel ore.
95% of sulphidic nickel ores are mined underground in depths between 200m and 1800m, the ore is transferred to the beneficiation. Widening of the tunnels is mainly done by blasting. The overburden – material, which does not contain PGM-bearing ore – is deposed off-site and is partially refilled into the tunnels.
Emissions: The major emissions are due to mineral born pollutants in the effluents. The underground mining operations generate roughly 80 % of the dust emissions from open pit operations, since the major dust sources do not take place underground. Rain percolate through overburden and accounts to metal emissions to groundwater.
Waste: Overburden is deposed close to the mine. Acid rock drainage occurs over a long period of time.
After mining, the ore is first ground. In a next step it is subjected to gravity concentration to separate the metallic particles from the PGM-bearing minerals. After this first concentration step, flotation is carried out to remove the gangue from the sulphidic minerals. For neutralisation lime is added. In the flotation several organic chemicals are used as collector, frother, activator, depressor and flocculant. Sometimes cyanide is used as depressant for pyrite. Tailings usually are led to tailing heaps or ponds. As a result, nickel concentrates containing 7 - 25% Ni are produced.
Emissions: Ore handling and processing produce large amounts of dust, containing PM10 and several metals from the ore itself. Flotation produce effluents containing several organic agents used. Some of these chemicals evaporate and account for VOC emissions to air. Namely xanthates decompose hydrolytically to release carbon disulphide. Tailings effluent contains additional sulphuric acid from acid rock drainage.
Waste: Tailings are deposed as piles and in ponds. Acid rock drainage occurs over a long period of time.
METALLURGY AND REFINING:
There are many different process possibilities to win the metal. The chosen process depends on the composition of the ore, the local costs of energy carrier and the local legislation. Basically two different types can be distinguished: the hydrometallurgical and the pyrometallurgical process, which paired up with the refining processes, make up five major production routes (See Tab.1). All this routes are covered, aggregated according to their market share in 1994.
Pyrometallurgy. The pyrometallurgical treatment of nickel concentrates includes three types of unit operation: roasting, smelting, and converting. In the roasting step sulphur is driven off as sulphur dioxide and part of the iron is oxidised. In smelting, the roaster product is melted with a siliceous flux which combines with the oxidised iron to produce two immiscible phases, a liquid silicate slag which can be discarded, and a solution of molten sulphides which contains the metal values. In the converting operation on the sulphide melt, more sulphur is driven off as sulphur dioxide, and the remaining iron is oxidised and fluxed for removal as silicate slag, leaving a high-grade nickel – copper sulphide matte. In several modern operations the roasting step has been eliminated, and the nickel sulphide concentrate is treated directly in the smelter.
Hydrometallurgy: Several hydrometallurgical processes are in commercial operation for the treatment of nickel – copper mattes to produce separate nickel and copper products. In addition, the hydrometal-lurgical process developed by Sherritt Gordon in the early 1950s for the direct treatment of nickel sulphide concentrates, as an alternative to smelting, is still commercially viable and competitive, despite very significant improvements in the economics and energy efficiency of nickel smelting technology. In a typical hydrometallurgical process, the concentrate or matte is first leached in a sulphate or chloride solution to dissolve nickel, cobalt, and some of the copper, while the sulphide is oxidised to insoluble elemental sulphur or soluble sulphate. Frequently, leaching is carried out in a two-stage countercurrent system so that the matte can be used to partially purify the solution, for example, by precipitating copper by cementation. In this way a nickel – copper matte can be treated in a two-stage leach process to produce a copper-free nickel sulphate or nickel chloride solution, and a leach residue enriched in copper.
Refining: In many applications, high-purity nickel is essential and Class I nickel products, which include electrolytic cathode, carbonyl powder, and hydrogen-reduced powder, are made by a variety of refining processes. The carbonyl refining process uses the property of nickel to form volatile nickel-carbonyl compounds from which elemental nickel subsides to form granules. Electrolytic nickel refineries treat cast raw nickel anodes in a electrolyte. Under current the anode dissolves and pure nickel deposits on the cathode. This electrorefining process is obsolete because of high energy demand and the necessity of building the crude nickel anode by reduction with coke. It is still practised in Russia. Most refineries recover electrolytic nickel by direct electrowinning from purified solutions produced by the leaching of nickel or nickel – copper mattes. Some companies recover refined nickel powder from purified ammoniacal solution by reduction with hydrogen.
Emissions: In all of the metallurgical steps, sulphur dioxide is emitted to air. Recovery of sulphur dioxide is only economic for high concentrated off-gas. Given that In the beneficiation step, considerable amounts of lime are added to the ore for pH-stabilisation, lime forms later flux in the metallurgical step, and decomposes into CO2 to form calcite. Dust carry over from the roasting, smelting and converting processes. Particulate emissions to the air consist of metals and thus are often returned to the leaching process after treatment. Chlorine is used in some leaching stages and is produced during the subsequent electrolysis of chloride solution. The chlorine evolved is collected and re-used in the leach stage. The presence of chlorine in wastewater can lead to the formation of organic chlorine compounds (AOX) if solvents etc. are also present in a mixed wastewater. VOCs can be emitted from the solvent extraction stages. A variety of solvents are used an they contain various complexing agents to form complexes with the desired metal that are soluble in the organic layer. Metals and their compounds and substances in suspension are the main pollutants emitted to water. The metals concerned are Cu, Ni, Co, As and Cr. Other significant substances are chlorides and sulphates. Wastewater from wet gas cleaning (if used) of the different metallurgical stages are the most important sources. The leaching stages are usually operated on a closed circuit and drainage systems, and are therefore regarded as minor sources.
In the refining step, the combustion of sulphur leads to emissions of SO2. Nitrogen oxides are produced in significant amounts during acid digestion using nitric acid. Chlorine and HCl can be formed during a number of digestion, electrolytic and purification processes. Chlorine is used extensively in the Miller process and in the dissolution stages using hydrochloric acid and chlorine mixtrues respectively. Dust and metals are generally emitted from incinerators and furnaces. VOC can be emitted from solvent extraction processes, while organic compounds, namely dioxins, can be emitted from smelting stages resulting from the poor combustion of oil and plastic in the feed material. All these emissions are subject to abatement technologies and controlling. Large quantities of effluents contain amounts of metals and organic substances.
Waste: Regarding the metallurgical step, several co-products, residues and wastes, which are listed in the European Waste Catalogue, are generated. Some of the process specific residues can be reused or recovered in preliminary process steps (e. g. dross, filter dust) or construction (e. g. cleaned slag). Residues also arise from the treatment of liquid effluents, the main residue being gypsum waste and metal hydroxides from the wastewater neutralisation plant. These residuals have to be disposed, usually in lined ponds. In the refining step, quantities of solid residuals are also generated, which are mostly recycled within the process or sent to other specialists to recover any precious metals. Final residues generally comprise hydroxide filter cakes (ironhydroxide, 60% water, cat I industrial waste).
Kerfoot D. G. E. (1997) Nickel. In: Ullmann's encyclopedia of industrial chemis-try (ed. Anonymous). 5th edition on CD-ROM Edition. Wiley & Sons, London.