Leaching, agitation temperature

Agitated autoclaves These systems are used for leaching under conditions of elevated temperatures and pressures... 

Static Leaching Test at room temperature, no agitation... 

The use of chemical modelling to predict the formation of secondary phases and the mobility of trace elements in the CCB disposal environment requires detailed knowledge of the primary and secondary phases present in CCBs, thermodynamic and kinetic data for these phases, and the incorporation of possible adsorp-tion/desorption reactions into the model. As noted above, secondary minerals are typically difficult to identify due to their low abundance in weathered CCB materials. In many cases, appropriate thermochemical, adsorption/desorp-tion and kinetic data are lacking to quantitatively describe the processes that potentially affect the leaching behaviour of CCBs. This is particularly tme for the trace elements. Laboratory leaching studies vary in the experimental conditions used (e.g., the type and concentration of the extractant solution, the L/S ratio, and other parameters such as temperature and duration/ intensity of agitation), and therefore may not adequately simulate the weathering environment (Rai et al. 1988 Eary et al. 1990 Spears Lee, 2004). 

For the first step, 12 g. of ground coal and 120 ml. of alkaline solution were mixed and placed in a 300-ml. stainless steel autoclave equipped with a turbine agitator. The system was flushed with nitrogen and then heated to the desired temperature while the mixture was stirred continuously. After a period of treatment at constant temperature and pressure, the autoclave was cooled quickly, and the contents were filtered to recover the coal. The filter cake was washed with 400 ml. of distilled water, dried at 90 C for 4 hr., weighed, and analyzed for total sulfur and ash. A portion of the alkali-treated coal (usually 2.5-3.0 g) was leached for an additional... 

Ultrasonic energy is frequently used to accelerate the dissolution of solid samples under soft conditions of temperature, pressure and chemical reagents. Similar to direct dissolution by agitation, US-assisted soft digestion is not used to the same extent as other operations of the analytical process such as leaching, derivatization or detection. The simplicity of this operation with some types of samples and the operator s lack of awareness of its error contribution are responsible for the absence of optimization studies for this process. Inappropriately conducted soft digestion can result in major errors and affect the quality of the results. 

The temperature and NHj coneentrations in the leach liquor have the most influence on the rate of leaching, followed by oxygen partial pressure and amount of agitation. A pregnant solution with sufficient thiosulfate and polythionate content must be produced to react with the copper present in the subsequent boiling stage. It must also be regulated to produce an iron oxide residue with very little absorbed nickel. 

The second and third steps are usually the rate-controlling steps. To enhance the solubility and minimize the mass-transfer limitations, the design of a leaching unit will have to take into consideration the effects of particle size, solvent, temperature, and agitation. 

The parameters that control the leaching process are as follows temperature, carbon dioxide pressure, agitation, slurry density, particle size, and leachant composition. In general the effects of these parameters on a slurry of Mg(OH)2 are as follows ... 

The sodium reduction of titanium tetrachloride was actually carried out as early as 1939 in Germany, and about 670 kg was produced by the Deutsche Gold and Silber Scheideanstalt, during the 1939-45 war. The process, now obsolete, involved reduction in a molten bath of 50 per cent sodium chloride and 50 per cent potassium chloride at 800°C in an atmos phere of hydrogen. The reactors consisted of expendable welded sheet-iron cylindrical vessels, 50 cm diameter by 70 cm deep and 2 mm thick. These rested loosely in a stout iron crucible, fitted into a gas-fired furnace. A portable stirrer was used to agitate the reactor contents. Approximately 20 kg batches of titanium were reduced by distilling 85 kg of titanium tetrachloride at a controlled rate into a melt of 15 kg sodium chloride and 15 kg of potassium chloride, covered with a layer of 46 kg of molten sodium. The titanium sank to the bottom of the molten salts, and at the end of the reaction was recovered from the crushed solidified melt by leaching with dilute hydrochloric acid, in a ceramic-lined vessel. It was finally washed in water and dried at a moderate temperature. The same plant was also used for the production of zirconium metal by the sodium reduction of potassium fluorozirconate (KaZrF ]. 

MBI Methylene Blue Index MCC Test. (Metodo Centro Ceramica) is a test for the surface abrasion resistance of glazed tiles, specified in BS 6431 Pt 20. It uses a dry abrasive, in contrast to the PEI TEST (q.v.) which is also specified. MCC - IP. Static Leach TesL Speciments of known geometric surface are immersed in selected leachants, without agitation, for defined time intervals at defined temperatures. The test has been applied to dental ceramics, with leach periods of 1,7,14 and 28 days at OO C, with leachants chosen to... 

The high-lithium brines usually have obtained most of their lithium from geothermal waters, with perhaps some of the lithium coming from surface leaching of volcanic ash, clays or other rocks. However, lithium is very difficult to leach from the lattice structure of all rocks and minerals, so little is dissolved imless the water is very hot. Experimental studies have shown that at ambient temperatures, only 55-170 ppb dissolves from extended contact with granitic rocks, but at 275-600°C 0.25-2.4 ppm Li can be extracted in the same agitated, long contact-period (Dibble and Dickson, 1976). Analyses of cores into deep-ocean rift or subduction zones... 

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