Leaching agent

Leaching Chemistry. The purpose of the leaching operation is to dissolve the desired mineral and separate it from the gangue material. The reaction should be selective and fast, the solvent inexpensive or easHy regenerated. Several leaching agents are commonly used. 

Laugemittel, n. leaching agent, laugen, .t. lye, steep in l.ye buck leach, lixiviate. — gelaugte Saure, (Paper) tower liquor to which has been added liquor from the cookers (in the sulfite process). 

Results of the leaching experiments at 25°C are more difficult to interpret. Basalt ground water is not the most effective leaching agent nor is shale the least effective. It appears that at the lower temperature fluoride plays a minor role and other, less obvious, factors predominate. Some of the differences could result from kinetic effects. This is a continuing study with further sampling scheduled at still longer time periods, so it is possible that later results will help clarify the 25°C data. 

For pure water, [H+] = [OH ] and pH = 7. Any solution with pH = 7 is by definition a neutral solution. No matter what other solutes occur in a given solution, the product of hydrogen and hydroxide ion activities will always be 1CT14 at 25 °C. This may be noted that the value of this equilibrium constants alter with temperature, as do all equilibrium constants. For this reason at 230 °C, K = 10 11/1 and a neutral solution would have a pH of 5.7. This brief diversion specifically focusing attention on the ionic compositional aspects of water is quite relevant with regard to its role played as a leaching agent. 

Cavitation collapse will generate shock waves which can cause particle cracking through which the leaching agent can enter the interior of particle by capillary action... 

These elements are noble metals and, as such, can be dissolved only with great difficulty. The usual leaching agent is hydrochloric acid, with the addition of chlorine to increase the solution oxidation potential. This strong chloride medium results in the almost exclusive formation of aqueous chloroanions, with, under certain circumstances, the presence of some neutral species. Very seldom are cationic species formed in a chloride medium. However, these elements do possess a range of easily accessible oxidation states and, with the possibility of a number of different anionic complexes that are dependent on the total chloride concentration, this provides a very complicated chemistry. A summary of the most important chloro complexes found in these leach solutions is given in Table 11.6, from which the mixed aquochloro and polynuclear species have been omitted. The latter are found especially with the heavier elements. 

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