Leaching steps

In the hot leaching step, barium metasiUcate is insoluble, and the orthosiUcate yields only one-half of its barium value to give barium hydroxide... 

Many industrial processes begin with a leaching step, yielding a slurry that must be clarified before solvent extraction. The solid-liquid separation is a costly step. The solvent extraction of unclarified liquids ( solvent-in-pulp ) has been proposed to eliminate solid-liquid separation. The increased revenue and reduced energy cost make this an attractive process, but many problems remain to be solved loss of metals and extractants to the solid phase, optimization of equipment design, effluent disposal, etc. 

The process used for recovery of uranium from its ores depends on the nature of the ore. All the processes include a leaching step that solubilizes the metal. Solvent extraction is used most frequently for the recovery and... 

Excess ammonia is evaporated from the resulting extraction raffinate and zinc is precipitated as carbonate by the remaining ammonium carbonate in the solution or by addition of carbon dioxide. The evaporated ammonia is absorbed in the filtrate and recycled to the leaching step. 

After shaping, the articles are most often subjected to a step to remove the processing oil or solvent from the gel. An extraction, washing, or leaching step is introduced in order to remove the processing oil and the lubricant (36). In formulations with filler, the extruded sheets are preferably subjected to an extraction step to remove processing oil. 

The applied leaching procedure [TESSIER et al., 1979] shows some lack of precision resulting from nonselective extraction, nonexactly definable phases in the environmental river compartment, and possible readsorption after the leaching steps [KHEBOLAN and BAUER, 1987 SAGER et al., 1990 TESSIER and CAMPBELL, 1990], No leaching sequence yet exists for definite discrimination of different metal species. 

In the processing of 100 metric tons of coal having a 1.0% sulfur content, how much limestone (CaC03) must be decomposed to provide enough Ca(OH)2 to regenerate the NaOH used in the original leaching step ... 

To determine the effect of the final temperature during the alkaline leaching of Cherokee coal, several runs were carried out in which different portions of the coal were treated with 1.0 M Na2C03 for 1.0 hr. at various final temperatures. The alkali-treaTed coaT was then leached with HN03. The results of the alkaline leaching step are indicated in Figure 3 and the overall results in Figure 4. 

The presence of lead and cadmium in the cement matrix with those concentrations did not lead to decreasing of samples strengths. Lead showed better improvement in stabilization and then cadmium. Lead dissolution at low pH values corresponded closely with the loss of aluminum, suggesting an ettringite or ferrite stabilization mechanism. The leachability of cadmium is continuous as the pH decreases from 9.5 to lower values during the batch leaching steps, and confirms a simple insoluble hydroxide stabilization mechanism and pH-controlled dissolution. 

If NaOH is the alkali used in the leaching step the dissolution of zinc is given by... 

The importance of waste reduction through the use of a chemical catalyst can be exemplified by the use of yV-methylimidazole as a catalyst in the leaching step of gold extraction from ores in the mining industry. Cyanide, a toxic substance that poses a major health threat, has traditionally been used for these processes. A sample case is the 1999 leak in a Rumanian facility from a cyanide storage tank into the Rhine River that killed thousands of fish. 

Also incorrect was the use of slurry to refer to the treatment of biological samples in a 3% nitric acid solution that were subject to US in autosampler cups prior to transferring the supernatant to an ETAA spectrometer [29]. This was clearly a US-assisted leaching step that took place in autosampler cups. 

The duration of a leaching step is dictated by both solubility mechanisms and transport phenomena. Careful selection of the leachant plays a key role in three crucial steps of the leaching process, namely ... 

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