Hydrometallurgical Operations

The copper powder is separated by decanting the reduction end solution in the settling tank. The copper powder slurry is centrifuged and washed. 

The high-purity powder contains about 15 wt. % water and 0.05-0.1% carbon from the decomposition of polyacrylic acid used in the reduction autoclaves. Drying the copper powder in the presence of 2-3 wt. % oxygen is necessary to accelerate the removal of carbon during the sintering under an atmosphere of hydrogen. 

The metal values associated with other minerals but not amenable to separation and concentration by the standard beneficiation techniques such as flotation can usually be recovered by chemical methods. The Climax Molybdenum process to recover the molybdenum oxide values associated with the sulfide ore and the Union Carbide process for the separation of molybdenum from tungsten in a floatation concentrate are in this category. 

The processing of nickel oxide ores is illustrated by the sulfuric acid leaching of nickeliferous laterites and the precipitation of high-purity nickel and cobalt powder by reaction with hydrogen gas giving ammonium sulfate as by-product. This process is in use at Moa Bay, Cuba. 

The leach liquor containing the dissolved metal values is separated from the residue containing iron oxide and other insolubles by thickeners and disc filters. All soluble nickel from the leach residue is recovered by careful washing, repulping, and filtering procedures before being discarded to 

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Apart from pyrometallurgy, the various ingredients of heterogeneous reaction kinetics are also very pertinent to several hydrometallurgical operations. This will be discussed in Chapter 5. 

The text so far has pertained mostly to energy- and environment-related considerations that are relevant to certain representative pyrometallurgical and electrometallurgical operations. The present section deals more generally with such considerations in the context of hydrometallurgical operations. 

Although these hydro-based processes, when applied to sulfidic sources, do not cause air pollution due to sulfur dioxide emission, they - and many other hydrometallurgical operations that are generally used for a wide variety of raw materials and resources - can create both land and water pollution problems. 

Jarosite [Named after the mineral, first recognized at Jarosa, Spain] A process for removing iron from the leach liquors from hydrometallurgical operations. First used in 1964 in processing zinc sulfate liquors at Asturiana de Zinc, Spain. Also used for recovering zinc from the residues from the electrolytic zinc process. See also Goethite, Haematite. 

The economic outcome of the operation of a centrally located facility is comparable with all other hydrometallurgical operations and is highly dependent on price and quality of the metals produced. All products have to conform to commercial specifications. Adequate quality and quantity of cheap feed materials are also essential. It is very important to consider the fact that the transformation of waste and raw material usually involves a dramatic increase in the value of the feed material. The economic result cannot be isolated to an auxiliary process, but is the result of the combined effects on the total operation. 

Tri-n-butyl phosphate and di-2-ethyIhexyl phosphoric acid (HDEHP) have been mainly used as extractants in several hydrometallurgical operations in the nuclear fuel cycle. Shukla and Mishra [27] have studied the extraction as well as transport behavior of uranium through BLM using 40% TBP in dodecane. The transport of by TBP at the feed-membrane... 

During the last two decades, pressure-driven membrane processes namely reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF) have found increased applications in water utilities and chemical industries. Unlike RO, NF, and UF, the Donnan membrane process (DMP) or Donnan dialysis is driven by an electrochemical potential gradient across an ion-exchange membrane. Theoretically, the DMP is not susceptible to fouling because particulate matter or large organic molecules do not concentrate on the membrane surface, as commonly observed with pressure-driven membrane processes. DMP has been used in the past in hydrometallurgical operations [19,20], for concentration of ionic contaminants [21,22] and for separation of... 

As mentioned previously, most of the wastes from hydrometallurgical operations are simply treated and then sequestered in tailings impoundments. For those operations that do not have tailings impoundments, more complete process scenarios have had to be designed. For nearly every operation, pretreatment wastewaters, rinse waters, or wash waters must include neutralization and metal removal before the solutions can be discharged, impounded, or reused. The most widespread method for removing dissolved metals from solution is to precipitate them as solids for separation. 

The pyrometallurgical operation presents different advantages compared to the direct exportation of cobalt ore. It allows a reduction, by a factor 5 - 6, of the weight to be transported. It also allows substantial reduction of reagent during hydrometallurgical operations, in particular due to the reduction of the Mn / Co ratio in the white alloy and due to the reduction of the content of acid consuming minerals in the ore (dolomite, calcite, e.g.). 

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