Leaching operating conditions

At the heart of a leaching plant design at any level—conceptual, pre-liminaiy, firm engineering, or whatever—is unit-operations and process design of the extraction unit or hne. The major aspects that are particular for the leaching operation are the selection of process and operating conditions and the sizing of the extrac tion equipment. 

Process and Operating Conditions The major parameters that must be fixed or identified are the solvent to be used, the temperature, the terminal stream compositions and quantities, leaching cycle (batch or continuous), contact method, and specific extractor choice. 

The zinc circuit consists of a similar pH-controlled leach at 60°C under oxidizing conditions. Zinc fine dust with low copper content is leached with the copper barren raffinate and with part of the zinc raffinate. The zinc leaching operation is maintained at about pH 2 for most of the leaching time and then slowly raised to a final pH of 4.5, reducing the iron level to below 10 ppm. The leach solution is filtered and cleaned from impurity metals such as Cu, Ni, and Cd by an ordinary cementation procedure, again filtered and finally fed to a solvent extraction circuit. Zinc is extracted in three stages with... 

The leaching conditions of a ultrasound-assisted device were studied to obtain the best experimental settings Microwave acid extraction was implemented to recover metals from solid materials. The operational conditions needed to form the hydrides were set after ana-... 

Polychlorinated biphenyls (PCBs) are also frequently included in pollutant monitoring programmes owing to their substantial persistence and accumulation in the environment. This has raised the need to develop methods for their routine analysis. USAL as a sample preparation method is an effective choice for the fast, efficient and straightforward removal of these compounds, as shown by the method for the determination of 146 PCBs in heron eggs [119], where ultrasonic leaching resulted in improved precision, efficiency and reliability under the operational conditions proposed. USAL was used prior to the... 

We have demonstrated the importance of system component compatibility and manufacturing variables using examples from our product development experience (figure 12.12)." 3 Other groups have also shown the effects of non-MEA components on stack life. Stack components must be chemically and mechanically stable under fuel cell operating conditions so that they will not leak or leach out species that poison the electrode catalysts, be harmful to membrane stability and its proton conductivity, or have adverse effects on the electrode/GDL properties, such as hydrophilic/hydrophobic character. Stanic and Hoberecht linked membrane edge... 

Under certain conditions, there are definite advantages in using hydrochloric, nitric, or other acids to carry out a dissolution step. In their evaluation of proposed processes for the recovery of alumina, Peters ei al. (P8) cited earlier experimental work which showed that both hydrochloric and sulfuric acid are equally good in extracting alumina from calcined clay (TIO). In the separation of the leach liquor from the silica residue by filtration, the chloride solution rapidly separated, while the sulfate solution did not separate easily. In addition to ease of filtration, the hydrochloric acid leach also made the later removal of iron easier. The insolubility of titanium dioxide in hydrochloric acid also eliminated another separation problem. Under this particular situation, hydrochloric acid was the natural choice. As in most large leaching operations, the acid would be recovered and recycled. 

Fig. 6.14. Kinetic curves for six PAHs leached under optimum operating conditions by SDS-DPHSE and DPHSE. (Reproduced with permission of Elsevier.)...

Despite recent efforts toward settling operational conditions for metal and metalloid fractionation assays—in terms of concentration, pH, and temperature for each of the leaching reagents, sample weight/extractant volume ratio, extraction time, shaking protocol, analytical instrumentation, and phase separation method —conventional sequential extraction schemes lack automation and are inherently rather time consuming and laborious. This is the consequence of a number of steps needed for the separation, identification, and quantification of TEs in each fraction. For example, the SM T recommended protocol lasts more than 50 hours, whereas the operating time of Tessier s scheme approaches 20 hours. 

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