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| '''Leaching''' is the process of extracting minerals from a solid by dissolving them in a liquid, either in nature or through an industrial process. In the [[chemical process]]ing industry, leaching has a variety of commercial applications, including separation of [[metal]] from [[ore]] using [[acid]], and [[sugar]] from [[beet]]s using hot [[water]].
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| In a typical leaching operation, the solid mixture to be separated consists of particles, [[inert]] insoluble carrier A and [[solute]] B. The [[solvent]], C, is added to the mixture to selectively dissolve B. The overflow from the stage is free of solids and consists of only solvent C and dissolved B. The underflow consists of slurry of liquid of similar composition in the liquid overflow and solid carrier A. In an ideal leaching equilibrium stage, all the solute is dissolved by the solvent; none of the carrier is dissolved. The mass ratio of the solid to liquid in the underflow is dependent on the type of equipment used and properties of the two phases. | |
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| Leaching is the process by which inorganic, organic contaminants or radionuclides are released from the solid phase into the waterphase under the influence of mineral dissolution, desorption, complexation processes as affected by pH, redox, dissolved organic matter and (micro)biological activity. The process itself is universal, as any material exposed to contact with water will leach components from its surface or its interior depending on the porosity of the material considered.
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| One such reaction is:
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| :Ag<sub>2</sub>S + NaCN → Na[Ag(CN)<sub>2</sub>] + Na<sub>2</sub>S
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| ==Leaching processes for biological substances==
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| Many biological organic and inorganic substances occur in a mixture of different components in a solid. In order to separate the desired solute constituent or remove an undesirable solute component from the solid phase, the solid is brought into contact with a liquid. The solid and liquid are in contact and the solute or solutes can diffuse from the solid into the solvent, resulting in separation of the components originally in the solid. This separation process is called ''liquid-solid leaching'' or simply ''leaching''. Because in leaching the solute is being extracted from the solid this is also called ''extraction''. In leaching, when an undesirable component is removed from a solid with water, the process is called ''washing''.<ref name=Geankoplis>{{cite book|last=Geankoplis|first=Christie|title=Transport Process and Separation Principles|year=2004|publisher=Pretence Hall|location=NJ|isbn=978-0-13-101367-4|pages=802–817}}</ref>
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| In the biological and food processing industries, many products are separated from their original natural structure by liquid-solid leaching. An important process for example is the leaching of sugar from sugar beets with hot water. In the production of vegetable oils, organic solvents such as [[hexane]], [[acetone]], and/or [[ether]] are used to extract oil from nuts, beans and seeds.
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| In the pharmaceutical industry, many different pharmaceutical products are obtained by leaching plant roots, leaves, and stems.<ref name=Geankoplis/>
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| ==Leaching Processes for inorganic and organic materials==
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| Leaching is extensively used in metal processing industries. The useful metal may occur in mixtures with very large amounts of undesirable constituents, and leaching is used to remove the metals as soluble salts.<ref name=Geankoplis/> The use of acids is prevalent in the metal processing industry, Sulphates are normally used to remove metals from the solid phase, these produce harmful environmental byproducts such as sulphates.
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| ==Shrinking-core model==
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| As mentioned above when leaching a solid with a liquid the desired solid goes to the liquid phase while undesired solid remains. The removal of the solid as the liquid dissolves into the particle leads to a diameter of unleached core that shrinks with time. A mathematical model can be used for this process, derived using [[Fick's law of diffusion]] taking pore diffusion as rate limiting step:<ref>{{cite book|last=Seader and Henley|first=J.D. and Ernest J.|title=Separation Process Principles|year=2001|publisher=John Wiley & Sons inc.|location=U.K|isbn=978-0-471-46480-8|pages=639–641}}</ref>
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| :<math>t=\frac{\rho _Br_s^2}{6D_ebM_Bc_{A_b}} \left[ 1-3 \left(\frac{r_c}{r_s}\right)^2 + 2 \left(\frac{r_c}{r_s}\right)^3 \right]</math>
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| ==Environmentally friendly leaching==
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| Some recent work has been done to see if organic acids can be used to leach lithium and cobalt from spent batteries with some success. Experiments performed with varying temperatures and concentrations of [[malic acid]] show that the optimal conditions are 2.0 M/L of organic acid at a temperature of 90 °C.<ref>{{cite journal|last=Li|first=Li|coauthors=Jing Ge, Renjie Chen, Feng Wu, Shi Chen, Xiaoxiao Zhang|title=Environmental friendly leaching reagent for cobalt and lithium recovery|journal=International Journal of Integrated Waste Management, Science and Technology|date=March 16, 2010|volume=30|series=Waste Management|issue=12|pages=2615–2621|url=http://www.journals.elsevier.com/waste-management/#description|accessdate=Nov 2011}}</ref> The reaction had an overall efficiency exceeding 90% with no harmful byproducts.
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| :4 LiCoO<sub>2</sub>(solid) + 12 C<sub>4</sub>H<sub>6</sub>O<sub>5</sub>(liquid) → 4 LiC<sub>4</sub>H<sub>5</sub>O<sub>5</sub>(liquid) + 4 Co(C<sub>4</sub>H<sub>6</sub>O<sub>5</sub>)<sub>2</sub>(liquid) + 6 H<sub>2</sub>O(liquid) + O<sub>2</sub>(gas)
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| The same analysis with [[citric acid]] showed similar results with an optimal temperature and concentration of 90 °C and 1.5 molar solution of citric acid.<ref>{{cite journal|last=Li|first=Li|coauthors=Jing Ge, Feng Wu, Renjie Chen, Shi Chen, Borong Wu|title=Recovery of cobalt and lithium from spent lithium ion batteries using organic citric acid as leachant|journal=Journal of Hazardous Materials|date=2010-04-15|volume=176|issue=1-3|pages=288–293|url=http://www.sciencedirect.com/science/article/pii/S030438940901810X|accessdate=Nov 2011}}</ref>
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| ==See also==
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| * [[Leachate]]
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| ==References==
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| {{reflist}}
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| [[Category:Chemical processes]]
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| [[Category:Industrial processes]]
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They call me Kelley Higham and I completely adore this title. In my expert life I am a library assistant. Oregon is the only location I've been residing in. To bake is a thing that I'm totally addicted to. My spouse and I maintain a web site. You may want to check it out here: http://tinyfarm.hpage.com
Here is my website ... garden & home decor gifts