WINNING WITH WATER

IS relatively new science J. H. Canterford, Commonwealth Scientific and Industrial Research Organization offers some attractive xtractive metallurgy, the science of recovering metals and non-metals options for recovery of from their , may be divided into hydrovietallurgy and pyronietallur- low-grade, complex and gy. Whereas in , heat plays a major role, in hydrometallur- small-body ores, and Egy, solution in water (or, in certain cases, solvents other than water) is an essential feature. readily lends itself to Thus, hydrometallurgy generally involves converting the desired or outomation. metals in an , concentrate or intermediate product into a water-soluble form, followed by recovering from solution a more highly refined product. In certain cases, however, hydrometallurgy is used to remove easily-soluble waste or from an ore, leaving an insoluble concentrate. As Wadsworth [I]has pointed out, hydrometallurgy, with a history dating back some ti00 years, has only recently attained the status of a science. This compares with a 6,OOO-yew history for pyrometallur~T. Because many hydro processes require the use of electrical energy, the widescale commercial use of hydrometal- lurgy dates back only some 120 yews. The significance of hydro processes can be well illustrated by reference to the wide range of papers presented at the Third International Symposium oti Hy(Irometd1urg-y , held in 1YX3 I.! 1. Annual reviews, including those of Warren I .I 1, provide useful data on cun’ent de\c.loi)”irnts, while the personal viewpoints of i3urkin 14 I, Habashi 151, I’icketi~gand Canterforti I(;], and Weir arid Masters I;] may give those associated with research and development of hydro processes a new slant on their problems. I3ecause hydro processes are can-ied out at relatively low temperatures (2(L 250°C) compared with pyro processes (600-2,0OO0C), rates of lust be carried out on a large scale, and addition of extr; reaction are much slower and, in most cases, control the rocessing capacity is very costly. productivity of a given size of plant. Wadsworth and Miller Another advantage of hydrometallurgy is that it is we1 [SI provide an excellent review of the rates of a wide range of uited to low-grade and more-complex ores. This is impor hydro reactions. ant, because the world’s high-grade ores that are readill Conventional hydro processes consist of three basic steps: eneficiated into concentrates suitable for pyrometallurg 1. Dissolution () of the wanted constituents. re becoming depleted. 2. Purification of the metal-containing solution (). A good example is : Although about 70% of thc 3. Recovery of the dissolved metals. rorld’s production is presently derived from sulfide ores Fig. 1 shows a simplified flowsheet of a typical hydro pro- iainly by pyro techniques, the sulfide ores account for on11 cess. As can be seen, there are numerous methods applicable bout 30% of the known land-based reserves. It is obvioui for each of the basic processes, the actual combination cho- hat nickeliferous (containing nickel) laterites will becomc sen depending on many factors. (Cementation is a process of icreasingly used as the source of nickel. surrounding a solid with a powder and heating the whole so Other advantages of hydrometallurgy are: Processes arc that the solid is changed by chemical combination with the eadily carried out on a continuous basis, leading to readj powder; is the recovery of a metal via utomation and control; and sulfides can be eliminated in tht .) lemental form, rather than as sulfur dioxide. Of course, hydro processes suffer from several importan! Why choose hydrometallurgy? isadvantages. One d the most important is that they art There are a number of metals, alloys or oxides that can be nergy-intensive. Other disadvantages are: They involvt produced only by a hydro or a pyro process. Uranium oxide andling large volumes of often dilute but corrosive an( (U,O,) and steel, respectively, are good examples. How- ?metimes poisonous solutions; and they produce residue: ever, there are many ores and concentrates that can be iat are difficult to filter, wash and dispose of in an environ treated by a variety of both hydro and pyro techniques. ientally acceptable manner. The choice between hydrometallurgy and pyrometallurgy, During the late 1960s and early 1970s, much of the impetus and indeed between several alternative hydro processes, )r the development of new hydrometallurgical routes cam( involves consideration of many factors, some of which be- -om the need to treat nonferrous metal sulfide concen. come apparent only during pilot-plant operations. Non-met- mates. Pyro treatment of these concentrates to tht allurgical factors - including geographical location, avail- roduction of large volumes of sulfur dioxide. If this is no1 ability of manpower, water and power, and market xovered and converted to sulfuric acid, then the potentia requirements - have a marked influence on the choice be- nd real environmental problems associated with the gener. tween two competing processes. The situation is not normally one of hydrometallurgy versus pyrometallurgy, but one of establishing the most favorable process for a given ore in a given location. As we are required to process lower-grade and more-complex feed materials, as energy costs continue to spiral, and environ- mental constraints become more severe, many of the new- generation processes will tend to incorporate both hydro and pyro stages. The roastileach/electrowin (RLE) process for recovering metallic zinc from zinc sulfide concentrates repre- sents one of the best-known examples of a process with a pyro “front end.” At the present time, hydro and combined hydrolpyro processes are used to recover a wide range of metals and nonmetals, including the following: uranium, gold, alumina, Solvent extraction, ion exchange, zinc, nickel, cobalt, copper, the platinum-group metals, tita- Cementation, precipitation, nium, niobium, , zirconium, molybdenum, tung- crystallization sten, beryllium, the rare earths, boron, halite (NaCl), car- nallite (KMgCl3-6H20),and sulfur. It is generally recognized that one of the advantages of Cementation, gaseous reduction, hydrometallurgy compared with pyrometallurgy is that the electrowinning former can be used to process relatively small ore deposits, using relatively small processing plants. Hence it is possible to design and economically operate a portable, trailer- mounted hydro plant. Good examples are the so-called purificaoon Waste PURE (Portable Uranium Recovery Equipment) plant de- signed by Dravo [9], and the solvent-extractiodelectrowin- ning unit developed by Holmes and Naver Inc. [IO]. igure 1 - The basic concepts of a hydrometallurgical On the other hand, to be economic, most pyro processes rocessing route are shown in this hypothetical flowsheet

42 CHEMICALENGINEERING/OCTOBER a. iw lition of extra ation of acid rain from the emitted SO2 cannot be ignored. treatment to convert the desired metal into a leachable form, Many metallurgists, process engineers and corporate or to reduce gangue dissolution, that is, increase that it is well managers believed that alternative routes based on hydro- selectivity. For example, ammoniacal ammonium carbonate This is impor- ~netallurgywould solve many of the problems, particularly leaching of nickeliferous laterites is carried out with pre- at are readily it1 view of the fact that it was known that some of these reduced feed. wometallurgy routes were capable of converting sulfides to the more Research is continuing on the development of alternative environmentally acceptable elemental form of sulfur. leachants, purification reagents and operating procedures. t 70% of the Some went so far as taking the view that hydrometallurgy For example, there are several groups investigating the use sulfide ores, kvas the panacea of all environmental ills associated with the of thiourea as an alternative to cyanide for the dissolution of mount for only extractive metallurgical industry. In reality, the situation is gold from a range of ores, concentrates, secondary products It is obvious not clear-cut. On one hand, there have been significant and residues. Many would regard the replacement of envi- l will become j improvements in sulfur dioxide recovery procedures; on the ronmentally unacceptable cyanide with thiourea as a very 1 other hand, hydro routes often produce solid and liquid desirable change. 9ocesses are residues that are difficult to dispose of, as discussed Electrowinning is energy-intensive, and considerable ef- ling to ready previously. forts are being directed towards the development of alterna- unated in the tive routes - particularly hydrogen reduction of the dis- Process selection solved metal on a continuous basis. Solvent extraction and .a1 important At a first glance, Fig. 1 might suggest that the hydrometal- ion exchange have been used for many decades in analytical hat they are lurgist is faced with (a>a difficult choice to be made between chemistry, but were only adopted in hydrometallurgy about 'hey involve the numerous alternatives available for each stage, or (b) the twenty years ago. They are now regarded as standard hydro mosive and advantage of having a wide range of alternatives that could unit processes. uce residues be used for a given ore in a giien location. In fact, these various hydro technologies have advanced to I an environ- In reality, the position is somewhat different. For any the stage that some reagents (extractants and resins) are given ore, there are normally only two or three reagents that now being manufactured for a specific hydro feed-solution. 'the impetus are commercially applicable for, say, leaching. The type of This contrasts with the position about 10 years ago, when a routes came ieuchant that can be used is largely determined by the process had to be designed to produce feed solution that was lide concen- mineralogical form in which the desired metal occurs, by the compatible with the reagents then commercially available. leads to the mineralogical form of the gangue minerals, the cost and ease The table gives a selection of the leachants now in com- f this is not of reagent regeneration, and the types of metal recovery mercial use, together with the solution purification and he potential procedures that are appropriate. metal recovery procedures applicable. The versatility of I the gener- In some cases, it is necessary to carry out a pre-leach pyro hydrometallurgy is immediately apparent.

Table - Hydrometallurgical processes exist for a number of ores, with various leachants, purification and recovery procedures

Ore type Leachants PurNficatfon and recovery I Bauxite Precipitation, crystallization Cu oxide ores Cementation, solvent extraction, electrowinning Cu sulfide concentrates' Electrowinning Cu sulfide wastes Cementation, solvent extraction, electrowinning Cu dross Solvent extraction, precipitation, electrowinning Co sulfide concentrates Solvent extraction, electrowinning Co-Ni sulfide concentrates Solvent extraction, electrowinning Gold ores Activated carbon, ion exchange, solvent extraction, electrowinning Mo-W concentrates Solvent extraction, precipitation Ni sulfide concentrates Hz reduction Ni laterites' Precipitation, , HI reduction Ni laterites Hz reduction, precipitation PGM* concentrates Solvent extraction, ion exchange Rare earths Solvent extraction Ti oxides Precipitation, reduction Zn sulfide concentrates* Electrowinning Zn sulfide concentrates Electrowinning U ores Solvent extraction, ion exchange, precipitation, calcination U ores Na2C0, Solvent oxtr8ction, ion exchange, precipitation, calcination 'Pre-leach roast required. t 'Prsleach reduction required. 'Platinum group metal Process examples Occupational health and safety factors are substantially better. Although a large volume of water is used, it is In this section, three recently developed hydro processes continuously recycled with only minimal losses; water con- will be outlined, one (solution ) being a general con- servation is thus a significant factor in the use of solution cept, the other two being specific operations. The wide mining. applicability of modern hydro practice is described in detail Establishment times (required for planning, installation elsewhere [I ,3,5,11]. and commissioning of plant) are relatively short. Solution mining - Also known as in-situ leaching, solu- On the other hand, solution mining is not without its tion mining involves direct dissolution from an orebody. problems and disadvantages: Hence it avoids conventional mining procedures, where the 1. Scaleup factors are difficult to establish. ore is mined by open-cut or undergr,ound techniques and is 2. Prolonged operational periods are required because of brought to the surface, where it is processed. the low rates of mineral dissolution. Fig. 2 shows an idealized representation of the concept of 3. Recovery is incomplete because of contact problems; solution mining. The leachant is pumped into the ore zone, most orebodies are highly irregular in geometry. where it dissolves the appropriate minerals. The leachate is 4. There is the possibility of contamination of the ground- then pumped to the surface, the metal recovered, and the water outside the ore zone. leachant is regenerated and returned underground. The last point is of concern, especially to many of the The advantages of solution mining compared with conven- general public who do not have any technical training, partic- tional processes can be summarized as follows: ularly in the field of hydrology. In reality, solution mining is Capital and operating costs are reduced because the no more, and probably less, environmentally hazardous than technique is not labor- or equipment-intensive. other forms of mining and a wide variety of other industrial Solution mining is applicable to deposits that cannot be activities. economically treated by other routes because of the small- Although commercial solution mining is presently restrict- ness or location of the deposit. ed to the recovery of copper, uranium, sulfur, trona (sodium Solution mining can be used to recover the remnants carbonate), carnallite (a double chloride of potassium and from previously worked orebodies, as well as low-grade magnesium), and halite (sodium chloride), it will become deposits, so that it is significant from the efficient-use-of- more diversified in the future. Feasibility and technical-scale resources point of view. Because large tonnages of ore are studies are now in progress for the recovery of gold, nickel, not brought to the surface, there is only limited surface cobalt, zinc, vanadium, manganese, colemanite (calcium bo- disturbance, and this is returned to its original state quite rate), and other minerals. The concepts and potential of readily. solution mining are well described elsewhere [1,18,13]. Uranium leaching - An oxidant is normally required in I I the acid dissolution of uranium ores. This is because the Recovery circuit uranium in the ore minerals is mainly in the acid-insoluble tetravalent form. Dissolution involves oxidation of the urani- I- I um to the water-soluble hexavalent form. Ferric iron is the normal oxidant. U02 + 2Fe3' -+ UO;' + 2Fe" As can be seen, ferrous iron is a product of this reaction. In order to maintain the progress of the uranium-ore dissolu- tion reaction, it is necessary to re-oxidize the ferrous iron. The most common oxidants for this purpose are sodium chlorate and manganese dioxide (pyrolusite). Both of these oxidants, while quite efficient for ferrous iron oxidation, can to environmental problems. The products of the oxidation reactions, sodium chloride and manganous sulfate respectively, are discharged to the dam with the leach residue. Although the manga- nese concentration of the tailings liquor can be reduced by neutralization with lime, this is not the case with the chloride ion. The final disposal of the excess liquor from the tailings dam can pose significant problems. Over the last 10 years or so, Caro's acid (permonosulfuric acid, H,SO,) has attracted much attention as an alternative oxidant. It has several important advantages over the solid oxidants. It is a liquid that can be readily stored and metered and, most importantly, the product of its reaction is water, Figure 2 - Leachant is pumped into the ore zone where i.e., it is environmentally attractive. it dissolves the appropriate minerals in a confined permeable layer It is also economically attractive because, although sulfu-

44 CHEMICAL ENGINEERING/OCTOREH W.19% ,jc acid still has to be added for ferrous iron oxidation, the research and development has been to avoid the discharge of sulfuric acid consumption is only half what it would be if sulfur dioxide to the atmosphere when the concentrates are manganese dioxide, the most common oxidant, were used. processed by pyro or combined pyrolhydro processes. filoreover, the amount of lime that is needed for leach However, sulfur dioxide recovery routes have been sub- psidue neutralization is also significantly reduced. stantially improved over the same period. The cost of this Numerous laboratory leaching programs and several plant recovery and the need to market the sulfuric acid are addi- trials have now been carried out using Caro’s acid as an tional factors that must be taken into account in evaluating oxidant for uranium leaching and a number of other applica- the potential of an orebody and its development (see Fig. 3). tions, including the oxidation of manganese in zinc electro- Despite an extensive amountlof research and develop- winning circuits. ment, commercial operation of a zinc-sulfide-concentrate/ One of the first full-scale commercial plants using Caro’s oxygen-pressure-leach plant did not commence until 1981 acid is at the Queensland Mines uranium processing opera- [151. Some might conclude that this extended period of non- tion at Nabarlek, Australia. Lucas and eo-workers [14] pro- commercialization is inaicative of misplaced confidence in the vide an excellent description of the plant trials, and discuss viability of hydro processes. Hydrometallurgists would dis- the reduced capital and operating costs. The cost compari- agree with this outlook and would point to conservatism in sons are realistic because the Nabarlek operation was origi- the application of new technologies and to market forces as nally based upon the use of manganese dioxide as the oxi- more significant in determining the time scale of dant. Complete conversion to Caro’s acid was carried out by implementation. mid- 1983. Fig. 4 shows a simplified flowsheet of the Cominco zinc- Although the overall Nabarlek circuit is not substantially sulfide-concentrate/pressure-leach process, as practiced at different from those of numerous other uranium leaching Trail, British Columbia (photo, p. 41). Leaching is carried plants using sulfuric acid, the Nabarlek trials are of interest out at 145-155°C and a total operating pressure of 1,300 kPd in that they describe another facet of hydrometallurgy. That (750 kPa oxygen). The continuous discharge from the four- is. they are concerned with the development and commer- compartment autoclave consists of three phases: an aqueous cialization of a new reagent (Caro’s acid), rather than the acidic zinc sulfate solution; molten sulfur; and a solid phase development of a totally new flowsheet. This type of devel- consisting of leach residue, unreacted sulfides, reaction opment is very important in helping to reduce capital and products [particularly plumbojarosite, PbFes(S04)4(0H),,], operating costs. and some sulfur. Zinc pressure leaching - Pressure leaching of zinc sul- As can be seen from Fig. 4, sulfur recovery is by a fide has been studied on both laboratory and commercial combination of crystallization and flotation. The leach resi- scale for more than 30 years. Part of the incentive for this due is processed in other portions of Cominco’s operations,

Is thfjre a market for acid?

Consider hydrometallurgy :er the solid or sell to custom smelter ind metered on is water,

Figure 3 - Decision tree for processing a complex lead-zinc-copper sulfide ore leads to SIX possible courses of action

CHEMICAL ENGlNEERINCiOCTORER 28,1985 45

~T -. .. ~ .j .-. I while the spent electrolyte from the zinc electrowinning larly by improving regeneration and recycling techniques circuit is used to slurry fresh feed. Developing reaction conditions that produce an easily The Trail operation is the first hydro operation where filtered residue sulfide sulfur is converted to the elemental state, and recov- Improving “in-pulp” techniques (without separation of ered and sold as such. In the other processes that directly leach residue) Rese produce elemental sulfur - for example, the Duval CLEAR Recovering all by-products H)tll process [I61 - no attempt is made at this stage to recover Ensuring that environmental problems are minimized l’hesa the elemental sulfur in a usable form. Developing alternative concepts. sciencc Work by Cominco indicates that, as well as being applica- ment ble to “pure” zinc sulfide concentrates, the general concept Environmental considerations simp11 can be applied to “dirty” zinc sulfide concentrates with Even though hydro operations for recovery of metals from use a significant iron, copper and lead sulfide (pyrite, chalcopyrite primary sources do produce a range of liquid and solid proce and galena) contents. effluents that must be disposed of in an acceptable manner, used hydrometallurgy plays a significant role in a wide range of ment Materials of construction effluent treatment procedures. These involve ion exchange, In Refractory bricks provide excellent protection for contain- solvent extraction, electrowinning, and selective as well as aitlzdl ment vessels in pyro processes, but in hydro operations bulk precipitation. appra there is no universal construction material. A material such Not only do these procedures ensure that effluents do not have as mild steel is perfectly satisfactory where the conditions become an environmental !ability, they also generate in- zinc-a are such that a chemically-inert oxide film is formed on the come, since they actually represent a method of resource menc: surfaces of the vessels, pipes, etc. But under different conservation. It is also interesting to note that hydro proce- ment, conditions, an inert film may not form, and the mild steel will dures are used to treat effluents arising from all mining and evalu be rapidly corroded. An alternative construction material metallurgical operations. For example, the techniques avail- searc: must be found in such a case. able to the hydrometallurgist are used to treat mine waste- encou Extensive use is now made of various plastics, ranging water, off-gases and waste streams from many pyro opera- At from PVC to butadiene rubber and fiberglass-reinforced tions, and in secondary and tertiary metal-fabrication hdru polymers. These materials are used for pipes, leaching ves- processes. ar1d c3 sels, holding tanks, solvent extraction mixerlsettlers, elec- It is not possible or appropriate here to discuss in detail turn: trowinning cells, etc., both in the solid form and as liners. effluent treatment by hydro procedures. The literature is Mii Titanium metal, although costly, is suitable for autoclaves extremely extensive, but the readerjs directed to Refs. 18- solid when acidic, oxidizing chloride-based leachants are used. It 20 for some typical examples. Ref. 20 is of interest in that the valua should be pointed out at this stage, however, that not all - hydro operations require advanced materials of construc- CO-U .tion, and there are numerous operations in which concrete, si1 or even bitumen-coated wood, is satisfactory. Hydro plants are characterized by the substantial number of pumps of various capacities that are required for trans- porting large volumes of corrosive and erosive solutions and slurries. This means that pump design and sizing, as well as materials of construction, are vital. Heflin and Stone [I71 provide an excellent review on pump selection. I Cost reduction As would be expected, small improvements in reducing capital and operating costs are not going to influence manag- Purified ers to change from known pyro or hydro processes to a sulfur commercially untested hydro route. This means that major - 11 economic incentives must become available before hydro- metallurgy will gain widespread acceptance for oreskoncen- hydnr trates that are readily processed by pyro routes. How can this be done? As discussed elsewhere [6], the major costs associated with hydro processes are largely controlled by three fac- tors - reaction rates, solidfliquid separation, and energy II consumption. Thus, a significant amount of hydro research Leach and development is, or should be, directed towards the residue following goals: Increasing the reaction rate - Figure 4 - In pressure leaching, zinc and sulfur are Figu Reducing gangue (waste) mineral dissolution can t Reducing reagent costs and consumption rates, particu- seoarated from sulfide concentrates at a Dressure of 1.300 kPa -

46 CHEMICAL ENCINEERING~OCTOBERa, IWS process uses casein (itself often a troublesome waste produ have when designing, commissioning and operating a com- from the dairy industry) as an ion-exchange “resin,” after mercial plant. is cross-linked with formaldehyde. Because hydro processes are often applied to low-grade and/or complex ores, the feed material is often more complex Research in chemical and mineralogical terms than the concentrates Hydrometallurgy research is carried out with multiple aim used in pyro processes. Moreover, because rates of leaching These include the development of an understanding of ti reactions are slow, the influence of the relative reactivities of science of a particular process, and the commercial develo] the ore and gangue minerals is critical in determining opti- merit of a process applicable to a particular ore type. 1 mum processing conditions. In order to maintain process simple terms, the first approach anticipates the long-ten materials balance, the feed should be as uniform as possible. use of the scientific knowledge in the development of In order to fully appreciate the reactions being studied, process, whereas in the second case, scientific knowledge the hydrometallurgist has to have a close working relation- used to solve a particular problem associated with the trea ship with the minefalogist. The latter will have as tools X- ment of particular ore in a given process. ray diffraction (XRD), differential thermal and thermogravi- In commercially guided research, process choice may t metric analysis (DTA/TGA), image analysis, and optical and aided by the use of a decision tree. A good example of such a electron microscopy. approach is that of Barbery, Fletcher and Sirois [21],wh Thermodynamics - Thermodynamic calculations are have discussed the options for processing a complex lea( used by all metallurgists and chemical engineers to deter- zinc-copper sulfide ore. They consider that prior to con mine a wide range of properties, including heats of reaction, mencement of large-scale commercial research and develol solubilities, phase stabilities, etc. Use of properties such as ment, the decision tree shown in Fig. 3 must be carefull activity coefficients, equilibrium constants, distribution co- evaluated. Those carrying out the more fundamental rt efficients, Gibbs free energies, etc., allow the hydrometal- search have a greater freedom of direction. Their work 1 lurgist to predict, for example, which particular reaction will cncouraged and used by the more applied researchers. proceed under a given set of conditions. At this time, there are three main productive areas ( The equilibrium chemical relationships of species that l~ydrometallurgyresearch - mineralogy, thermodynamic make up a given system are best represented in two- or and computing. Let us look briefly at each of these fields i three-dimensional plots, commonly known as predomimnce- turn: area or stability diagrams. Mineralogy - Mineralogical characterization of all th A number of computer programs have been developed solid phases associated with hydro processes provides ir over the last 10-15 years to assist with the calculation and valuable information that the chemical engineer needs t plotting of the necessary data. In addition, computer banks of thermodynamic data are continually being upgraded. All of the thermodynamic studies, but particularly the stability diagrams, clearly demonstrate the complexity of the various phases that the hydrometallurgist works with. Computing - Hydrometallurgists make extensive use of __I solii/liquid computing facilities to analyze their results, develop reaction Residue separation models, and design and control plants. For the latter, mass and heat balances are complicated by the fact that most processes incorporate countercurrent flow paths including I Ironoxidation Oxidant recycling in order to maximize product recovery. There are some tens of computer-based models that de- scribe various hydro unit operations, particularly leaching [1,2,8].Most are based on careful analysis of experimental Alkali data derived from laboratory-scale studies. Correlation with commercial-scale operations is considerably more complex. This is a reflection of the reduced control the experimenter Solid/liquM has over the operation, and the influence of other non- Vdroxide cake measurable factors. Another recently introduced use of computers into hydro 1 solvent processes is online control of a specific unit operation. Al- - extracton though flowmeters and belt scales have been used, the Spent circuit introduction of online control into hydro plants has been electrolyte hampered until recently by the lack of suitable probes that Electrowinning provide reliable measurements in corrosive and abrasive circuit t- Co-Ni metal environments. (See Refs. 22-25 on computers and control.) The future The rapid development of technology in general means that many components of modern equipment quickly become

CHEMICAL ENGINEEHINGKKTOBER W, 1985 47 outdated. For example: the electronic components industry recovery of cobalt or gold, simply on a basis of metal value. uses many metals, ranging from copper to gold; jet engine There is no doubt that hydrometallurgy will continue to turbines are made from cobalt-containing superalloys; while play an expanding role in various aspects of extractive many industries use catalysts based on the platinum-group metallurgy. There are many fundamental areas that require metals. further examination, particularly under conditions that ap- The catalysts become “poisoned” and lose their activity, ply to commercial operations. Thus we require much more and so must be replaced. There are also wastes generated reliable data on heterogeneous kinetics in multiphase sys- when the above components are fabricated, such as metal- tems at high ionic strengths and at high temperatures. There containing etching solutions, sludges, turnings, and unus- is a need for improved solidfliquid procedures and improved able castings. ‘h this list can be added the large volumes of recycling techniques, and most important of all, there has to primary metallurgical wastes, including slimes, fumes, filter be a reduction in energy consumption rates. cakes, etc. [2,11,26].Fig. 5 shows how sludges from super- Hydrometallurgy involves many technologies: mineral- alloy milling-machine operations can be processed to sepa- ogy; analytical, inorganic, organic, physical and surface A prE rate Co, Ni, Cr and Fe. chemistry; and thermodynamics; as well as several branches ventiii The recovery and recycling of various metals from of engineering. Input from economists, environmentalists be e:: “wastes” of the primary and secondary metallurgical indus- and social and political scientists also must be considered. tries is becoming widespread. The techniques used range be si;; from the very simple, such as physical recovery of scrap Acknowledgements causil tinplate as a source of metallic iron for copper cementation, The author would like to thank his many colleagues in the am01 to complex pyro and hydro processes. mining and metallurgical industries, research institutes and The types of procedures that can be economically used universities for their support and helpful discussions. In code depend on three main factors - volume, metal value and particular, he would like to thank Dr. Tom Scott, formerly of are 5 transportation costs. 7% these must be added a consideration CSIRO, for his unveiling of hydrometallurgy as a science and terial of the availability of indigenous primary sources. Obviously, as a career. the recovery of copper is less advantageous than is the Kenneth J. McNaughton, Editor eva I II corre References 1. Wadsworth, M. E., Hydrometallur Past, Present and Fu$re, in Gilmore, A. J., The Recovery of Zinc from a M,he Water Con$$ng Small Hydrometallur%Research, DevegGnt and Plant Practice, 0s- Amounts of Alkali and Heavy Metals, Cmadmrr lt~tztideMraz9q Me&- Asare K. and Iler, J. D. editors, AIME (Amer. Inst. of Mining, /ulgicalBu/Lefin,Vol. 70, No. 780, 1977; pp. 142-146. Metall’kg&al and &tmleum E‘ngineers), New York, 1983; pp. 348. Slater, M. J., Lucas, B. H., and Ritcey, G. M., Use of Continuous Ion 2. Osseo-Asare, K., and Miller, J. D., editors, “Hydrometallurgy: Researcii, Exchange for Removal of Environmental Contaminants from Waste Development and Plant Practice,” AIME, New York, 1983. ,Streams, Cailadiaii Znstifute Miriirq Metalluculyical BuUetiii, Vol. 71, 3. Warren, G. W., Hydrometallurgy - 1984, Review and Preview, J. / NO.796, 1978; pp. 117-123. Vol. 37, No. 4, 1985, pp. 59-62. 20.; Davey, P. ‘E, Houchin, M. R., and Wmter, G., Recovery of Chromium from Waste Electroplatin Liquors by Ion-Exchange on Casein, Fht 1, 4. Burkin, A. R., Hydrometallurgy 1952-1982: A Quiet Revolution, Ch?+ ,’ Pilot Plant Studies, J. 8kuicaL Tech~toOCosyBzohchnology, Vol. 33A, Id,1983, No. 18, pp. 690-695. ’, 1983; pp. 164-170. 5. Habashi, I?, Hydrometallurgy, Ck.Eiq. Nacs, Vol. 60,1982; pp. 4% El. Barbe G Fletcher A W, and Sirob, L. L., Exploitation of Complex 58. Sulphiz D&osits: A hew of Processing Options from Ore to Metals, in 6. Pickering, R. W., and Canterford, J. H., Hydrometallur Present and “Com lex Sulphide Ores,“ Jones, M. J.. editor, Institution of Mining and Future, in “Mineral Resources of Australia,’’ Key,D. GdWoodcock, Medurgy, London, 1980; pp. 135-150. J. T, editors, Australian Academy of ’khnologd Sciences, Parkville, 22. kbull, A. G:, A General Computer Pro for the Calculation of 1979; pp. 226-238. Chemcal Equhhna and Heat Balances, CAf?%W, Vol. 7, No. 2, 1983, 7. Weir, D. R., and Masters, I. M., The Interrelationship of Mineralogy, Pergamon Press, Elmsford, N.Y., pp. 137-147. Mineral Dressing, and Hydrometallur in Process Selection, 85th Annual 23. McGrew, K. J., and Richardson, J. M., Com uter Analysis of Metallurgical General Meeting, Canadian Institute o%iningand Metallurgy, Winnipeg, Reactor Stage Capacity, Met.., Vol. 12, 1981; pp. 26-30. 1983. J. 33, d. 24. Richardson, J. M., Coles, D. R.. and White, J. M., Fluor Mining and 8. Wadsworth, M. E., and Miller, J. D., H?rprometall ’cal Processes, in Metals Inpduces FLEXMET, a Computer-Aided and Flexible Metallur- “Rate Processes of Extractive Metall Sohn, H.? and Wadsworth, gical ’khruque for Steady-State Flowsheet Analysis, Eng. Mrn. J., Vol. M. E., editors, Plenum Press, New Yzl979; pp. 133-244. 182, No. 10, 1981; pp. 88-97. 9. McGarr, H. J., and Dement, E., ‘PURE’ Recovers Uranium from 25. Brown, M. C., and Bhappu, R. B., Recent Trends in Instrumentation of Small Deposits, Eng. Min. J., Vol. 179, No. 9, 1978; pp. 214-216. Hydrometallurgical Plants, in “Hydrometall Research, Development 10. Wey, J. N., and Faige, P. M., Can Electrowinning Replace Cement and Plant Practice”, OmAsare, K., and M%r, J. D., editors, AIME, Copper?, E7q. Min. J.,Vol. 173, No. 7, 1972; pp. 94-96. New York, 19%; pp. 739-757. 11. Kuhn, M. C., editor, “Process and Fundamental Considerations of Selected 6 Warson D. Recovery of Cobalt from Metall cal Wastes, in “F‘mceed- Hydrometallurgical System,” AIME, New York, 1981. ings In&rn&mal Conference on Cobalt,” AT$%r~s~els.Vol. 1, 1981; pp. 12. Canterford, J. H., Solution Mining - General Principles and Australian 139-148. Practice, in “Jobson’s Minin Year Book 1W84,” Dun and Bradstreet, Melbourne, 19%; pp. 215-22f 13. Schlitt, W. J., and Hiske J. B., editors, “Interfacing Technologies in Solution Mining,” AIME, hew York, 1W. ,aTheauthor 14. Lucas, G. C., Fulton, E. J., Vautier, F. E., Waters, D. J., and Ring, J. H. Canterford obtained B.S. and Ph.D. degrees in R. J., Queensland Mmes Plant Wswith Cam’s Acid, Pmc. A~tmlou. inorganic chemistry from the University of Mel- Zrcsf. Mi9i. Mefallutgy, No. 287, 1983; pp. 27-34 bourne. After four years on the staff of the Dept. of 15. Farker, E. G., McKa , D. R., and Salomon-DeFrieberg, H., Zinc Pressure Inorganic Chemistry at that university, he joined the Leaching at COMIN~OS’hail Operation, in “Hydrometallur~Research, Commonwealth Scientific and Industrial Research Or- Development and Plant Practice,” OsL-Asare, K., and Iller, J. D.. anization, Div. of Mineral Chemistry. PO. Box 124, editors, AIME, New York, 1983; pp. %-NO. ‘ia rt Melbourne. Victoria 8207, Australia. He is at present principal research scientist and hydrometal- 16. Atwood, ,G. E., and Livingston, R. W,The CLEAR Process, A Duval urgy group leader. Canterford is an associate of the Corporation Development, En?neta/l,Vol. 33, 1W; pp. 251-255. Royal Australian Chemical Institute, a member of the 17. Heflin, T R.. and Stone, D. B.,H~drqmet;rllyd Pumps - Materials Soc. of Mining Engineers and The Metallurgical Society (both sections of the and Design, Cailodian Znstztutt? z7wq Meta lulgy Bullehn, Vol. 72, Amer. Inst. of Mining, Metallurgical and Petroleum Engineem), and a mem- No. 809, 1979; pp. 122-127. ber of The Australasian Institute of Mining and Metallurgy.

48 CHEMICAL ENGINEERINGIOCTOBERB, iw