Introduction INTEC ZINC TECHNOLOGY A paper for the First International Conference on Mining, Mineral Processing, Metallurgical and Environmental Engineering Zanjan, 1517 September, 2013 D. Sammut, Project Manager, Intec Ltd The term Intec Process describes a suite of related technologies for the production of highgrade metals from mineral and industrial waste feedstocks, including both sulphide and oxide concentrates and residues. The key to the technologies is the use of halide leaching, typically chloride and/or bromide depending, which enables faster, more complete metal extraction at atmospheric pressure and temperatures below 100 C. Since 2004, development of the Intec Process has been primarily directed to the extraction and recovery of zinc and lead from various sources (including both sulphide and oxide minerals, electric arc furnace dust and galvanising industry spent pickle liquor), as well as gold from mineral concentrates. Applications have also been developed for copper and rare earth elements (particularly neodymium and dysprosium). The Intec Process Technology The Intec Process technology consists of a closedloop cycle of four processing steps: Leaching, Purification, Product Recovery and Acid Regeneration. Metalsbearing feed Leach Recycle Purify $ ByProducts Recover $ Metals The key to Intec s advantages ultimately come from the leach. Fresh feedstock is slurried and fed to a cocurrent series of (typically three) agitated tanks at atmospheric pressure, where the economic metals are leached into solution.
ZnS + 2H + + ½O 2 Zn 2+ + S 0 + H 2 O (1) ZnO + 2H + ZnCl 2 + H 2 O (2) PbS + 2H + + ½O 2 Pb 2+ + S 0 + H 2 O (3) The Intec Process brine matrix typically uses a total halide concentration of 6 8 moles/litre, with a boiling point of 115 120 C. The chloride components are typically a mixture of sodium and calcium chloride; with the ratio depending on overall halide requirements for metal solubility, and the calcium required for sulphate precipitation. The conditions of the leach can be varied to selectively leach some minerals such as galena (PbS), while avoiding the leaching of gangue minerals such as pyrite. Alternatively, the conditions can be increased to leach more refractory minerals, such as the zinc ferrites in electric arc furnace dust or goldbearing enargite. As economic target metals are often hosted in ironmineral matrices (such as zinc in ferrite or silicates), metal recovery is maximised by first leaching the minerals and then rejecting the iron into an environmentally stable hematite residue. Note that this hydrolysis reaction then partially offsets the overall acid requirement for leaching. ZnO.Fe 2 O 3 + 8H + Zn 2+ + 2Fe 3+ + 4H 2 O (4) Zn 4 (OH) 2 Si 2 O 7 + 8H + 4Zn 2+ + 2SiO 2 + 5H 2 O (5) 2Fe 3+ + 3H 2 O Fe 2 O 3 + 6H + (6) Although every application has its own unique aspects, the Intec Process can process a wider range of variability in the feedstock than competing technologies, as well as mixed feedstocks. It can offer particular advantages for the coprocessing of mixed sulphide and oxide feedstocks if direct electrowinning is included for product recovery, as the acid demands of the oxides can be balanced against acidgenerating capacity of the sulphides. Another advantage of halide hydrometallurgy is that there are a range of options for purification and recovery of byproducts, and for final recovery of target metal products. Byproducts can be recovered via simple ph adjustment as oxides or oxyclhorides (depending on conditions), via simple cementation using iron (with easy rejection of the resulting dissolved iron), via sulphide precipitation to yield mineral sulphide products equivalent to highgrade concentrates, or via other reactions as suggested by the individual feedstock(s). + CaCO 3 PbO + CaCl 4 2 + Fe 0 Pb 0 + FeCl 4 2 + CaS PbS + CaCl 4 2 + CO 2 (7 (8) (9) In each case, testing has proven that the resulting products can achieve high grades. Testing of live samples for equations (7) and (8) above, as example, has yielded >99% lead metal and up to 80% Pb in concentrate. The choice of recovery method then depends on the parameters and requirements of the individual project. Intec has demonstrated the direct recovery of Prime Western Grade zinc metal via direct
electrowinning, which can be particularly useful for sulphide feedstocks (which have an oxidant demand). (cathodic reaction) Zn 2+ + 2e Zn (10) (anodic reaction) 2Cl + Br BrCl 2 + 2e (11) Alternatively, the zinc can be extracted from the Intec electrolyte via conventional technologies to yield a hybrid process, which can be particularly useful for oxide feedstocks and/or where Special High Grade zinc metal product is required. Acid regeneration is then quite simple in the Intec Process due to the presence of background calcium. Via the addition of inexpensive sulphuric acid, the calcium balance in the process (versus alkali use during purification) is maintained. The resulting calcium sulphate production is controlled via known process conditions to yield either anhydrite, bassanite (hemihydrate) or gypsum (dehydrate), as best fit the local sales market for the byproduct. CaCl 2 + H 2 SO 4 + xh 2 O CaSO 4.xH 2 O + 2HCl (12) This results in a closedloop process in which the only minor losses are soluble salts associated with the washing efficiency of the residue filtration. Intec Process Advantages Overall, the Intec Process leaching technology has key advantages over competing technologies: Able to economically process lowgrade mineral concentrates Able to economically process polymetallic concentrates in a single process Able to process sulphide and oxide concentrates, singly or together Able to recover byproduct value from minor metals contained in concentrates Able to treat contaminated feeds, such as arsenicbearing concentrates No liquid effluents or atmospheric emissions High total extraction, often >99% of the target metal Short residence time, typically 24 hours Atmospheric leaching Low temperature of operation Hematitebased residues are clean, easily filterable and environmentally stable Together, these factors allow the Intec Process to utilise lowercost materials of construction, for smaller plant sizes and lower capital and operating costs overall. Experience with Operations All minerals processing projects are individual. Projects using conventional technologies require careful development for smooth operation and conservation of capital. An equally methodical approach is advisable in the implementation of any project incorporating new technology. Intec has therefore progressed its technology implementation through the necessary intermediate stages of pilot plant and demonstration plants, to bring it to its present state of commercial readiness and commercial project implementation.
Most notably, Intec s demonstration plant in Tasmania, Australia, was commissioned in 2006. It was used to prove the Intec Zinc Process application for a proposed project in Tasmania. (It is noted that the Hellyer Zinc project subsequently received the necessary government approvals for development, but stopped development in 2008 when the Global Financial Crisis caused 70% of Australia s zinc production to become uneconomic, and every Australian zinc operation either closed or was scaled back considerably). Using the Burnie Demonstration Plant, Intec has demonstrated the production of prime western grade zinc metal via direct electrowinning from the halide Since that time, the Burnie Demonstration plant has continued operations as a major test facility for developing Intec Process projects, as well as periodic commercial processing of zinc and leadbearing industrial wastes to yield mineral sulphide products. Together, Intec has accumulated a total of over ten years of accumulated operating experience, which provides a thorough body of proof of concept for the technology and materials of construction, as well as considerable engineering data for future projects. Economics of the Intec Process Every project is different, being influenced by scale, feedstock and location factors. For the purposes of this paper, the economic model for a proposed local project in Iran has been suggested, using local input factors as recommended to Intec. The proposed project utilises a hybrid flowsheet, with coleaching of zinc and lead using Intec Process technology, followed by conventional extraction to yield a solution suitable for electrowinning of Special High Grade zinc metal. The project is then divided into two stages: an initial throughput of 25,000tpa feedstock with rampup over 18 months, followed by expansion to 200,000tpa throughput, for the production of over 30,000tpa of zinc and lead metal. Equipment prices have been estimated on data from various studies completed for Intec of projects of similar size and scope, such as the Intec Hellyer Project studies completed by Intec and independent consulting engineering firms, WorleyParsons and ACSI. All estimates are taken from a Conceptual Study for the project completed in 2011.
The base case of the economic model predicts that the project offers a healthy economic return for the investment, with an internal rate of return (IRR) of 45%, based on a total capital investment of < US$7.50/t of installed zinc capacity. Operating costs for the Stage 2 development were estimated at approximately US$1,050/t of zinc alone, or <US$450/t of total metal production. Converting this to an operating cost per tonne of zinc after lead credits, the result was <$0. Put another way, the lead byproduct credits alone covered the costs of production, before zinc revenues were taken into account. Key operating cost centres for a project in Iran were primarily electricity for electrowinning (comprising nearly 50% of total operating cost), with transport and handling of feedstocks and products as the second major cost centre. Due to low labour costs in Iran, labour accounted for only 10% of total operating cost. However, this factor would be greater in other countries, particularly western countries such as Australia. Conclusion The Intec Process represents a paradigm shift in the extraction and recovery of metals, particularly from feedstocks that have proven intractable or uneconomic for conventional minerals processing technologies. The technology has been thoroughly demonstrated for the extraction and recovery of zinc from both oxide and sulphide resources, sourced from both mineral concentrates and industrial wastes. Based on considerable investment in the careful scalingup of technology through successive engineering phases, Intec has accumulated over 10 years of operational experience to be able to put forward the Intec Process as commerciallyready for largerscale minerals applications. This will extend and build upon Intec s current smallerscale commercial operations for industrial waste processing. The first commercialscale minerals project is currently under development in Iran, with Stage 1 planned to process 25,000tpa of feedstock to produce Special High Grade zinc metal and high purity lead metal, as well as byproduct values. The economics of this first project are very attractive. Further Reading As noted at the beginning of this paper, the Intec Process is also applicable to the extraction and recovery of other metals, and from differing feedstock types. The following is a list of useful papers describing the Intec Process applications for gold, copper, lowgrade mineral feeds and industrial wastes: Intec Gold Process, 2009 The Intec Copper Process, 2008 Intec: Technology Solutions for the Minerals Processing Industry, 2010 Making Light Work of Heavy Metals, 2010 A New Light for Heavy Metals, 2011