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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]]. | |||
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. | |||
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. | |||
One such reaction is: | |||
:Ag<sub>2</sub>S + NaCN → Na[Ag(CN)<sub>2</sub>] + Na<sub>2</sub>S | |||
==Leaching processes for biological substances== | |||
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> | |||
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. | |||
In the pharmaceutical industry, many different pharmaceutical products are obtained by leaching plant roots, leaves, and stems.<ref name=Geankoplis/> | |||
==Leaching Processes for inorganic and organic materials== | |||
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. | |||
==Shrinking-core model== | |||
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> | |||
:<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> | |||
==Environmentally friendly leaching== | |||
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. | |||
: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) | |||
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> | |||
==See also== | |||
* [[Leachate]] | |||
==References== | |||
{{reflist}} | |||
[[Category:Chemical processes]] | |||
[[Category:Industrial processes]] | |||
Revision as of 00:04, 26 April 2013
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 processing industry, leaching has a variety of commercial applications, including separation of metal from ore using acid, and sugar from beets using hot water.
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.
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.
One such reaction is:
- Ag2S + NaCN → Na[Ag(CN)2] + Na2S
Leaching processes for biological substances
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.[1]
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.
In the pharmaceutical industry, many different pharmaceutical products are obtained by leaching plant roots, leaves, and stems.[1]
Leaching Processes for inorganic and organic materials
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.[1] 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.
Shrinking-core model
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:[2]
Environmentally friendly leaching
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.[3] The reaction had an overall efficiency exceeding 90% with no harmful byproducts.
- 4 LiCoO2(solid) + 12 C4H6O5(liquid) → 4 LiC4H5O5(liquid) + 4 Co(C4H6O5)2(liquid) + 6 H2O(liquid) + O2(gas)
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.[4]
See also
References
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The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
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In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang
Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang