Leaching Tests in China.
Leaching Tests in India.
Leaching is the process in which any surface is deionized by rinsing it with acidic solution (Dorman & Dawes, 2012). The leached chemicals maybe organic or inorganic. For example, waste rubber tires are tested for leachment before recycling it into construction of road, artificial turf or embankment. While using rubber for these purposes, they release leachate to the ground. Thus, leaching test is performed for testing the release of leachate.
Leaching test, in general, involves rinsing or contacting the solid material with leachant (HCL or any other acid). The components in solid will dissolve in leachant and form a leaching solution. The governing factors can be determine by changing temperature, pH, concentration of leachant and time duration. This test provide information about the amount of released chemical from a waste material.
This literature review provides an overview about various application of leaching test and their relevance in environment, in Asian country like China and India. The international standards are adopted by many countries globally to administer testing procedures, evaluation and implication on environment.
Apart from the above mentioned application of leaching test, the process of leaching is also used in metallurgy. It is a cheap, efficient and eco-friendly method to extract gold, nickel, copper and uranium (Yin et. al., 2018). The Yangla Copper Mine in China uses heap leaching strategy due to poor output from tradition hydrometallurgy strategy. The copper ore have complex composition. Therefore, it contain variety of impurities. There are a lot of sulphides present in the ores along with high proportion of oxides. Copper sulphide ore is leached by sulphuric acid and significant passivation by substances such as jarosite is also possible (Malenga et al., 2015).
The leachate and its quantity is crucial while analysing pollution originating from municipal landfills. In China, due to high moisture content causes serious harm while taking precautionary measure against leachate (Yang et. al., 2015).
In chine, a large amount of fly ash and flue gas desulfurization (FGD) gypsum is produced from combustion residues of coal-fired power plant (Hao et. al., 2016). The FGD gypsum mostly ends up in landfills. The adverse effects of mercury found in fly ash was broadly investigated. An experiment was performed by Hao et. al., 2016, which uses the Synthetic Precipitation Leaching Procedure (SPLP) and Toxicity Characteristic Leaching Procedure (TCLP) to evaluate the toxicity caused by leaching of mercury (Hao et. al., 2016). The mercury in fly ash have adverse on the environment. The SPLP and TCLP tests were used to measure the leaching potential of mercury from FGD gypsum. The leachibility of solid waste in municipal landfills will be simulated by TCPL test in an acidic environment. The TCPL test. This test uses 17.25 ml of glacial acetic acid as the extraction fluid. This is then diluted with 1000 ml of deionized water maintaining the pH of 4.93 ±0.05. Then, one gram of FGD gypsum is added to the 20 ml of the solution. The samples were put in a centrifuge for 18 hours in a 50 ml tube, at room temperature, at tumbling speed of 30 RPM. After extraction, the sample were again put in centrifuge at 3000 RPM for 20 minutes, then it was filtered. 2% (v/v %) of 0.2 M BrCl was added to the filtrate for preservation and oxidization. Then CVAAS was used to determine the mercury concentration in the filtrate (Hao et. al., 2016). The SPLP test was carried out by using nitric acid and sulphuric acid to extract solid-waste for leaching toxicity test. The extraction fluid 20 ml was added with 2 gram of sample. Then rest of the procedure was similar to that of TCLP (Hao et. al., 2016). The conclusion of this experiment was that mercury is found in complex phase in FGD gypsum.
In India, the reuse of waste materials has become necessity because of new environmental regulations, which ensures minimal waste disposal. Steel manufacturing units face difficulties in disposing huge piles of waste generated while making steel (Chand et. al., 2016). An analysis was carried out by Chand et. al., 2016 showing the effect of short term leaching process like Batch Leach Test (BLT), Strong Acid Digestion Test (SADT), Toxicity Characteristic Leaching Procedure (TCLP) and American Society for Testing and Materials (ASTM) shake test. These test were carried out to check the leaching potentiality of heavy metals. Cd, Co, Fe, Mn, Pb, Zn, Se, As, Cr, V, Cu and Ni were the leachate from Linz-Donawitz (LD) slag waste (Chand et. al., 2016). The research was concluded as less heavy metal leaching by ASTM test, while relatively higher leachate from TCLP which indicate higher risk of pollution under acidic condition. The metal leaching depends on pH, extraction medium and solid to liquid ration. The LD slag characteristics like surface morphology, mineralogical composition and particle size also influences metal leaching. LD slag from steel plants are non-hazardous if the concentration of all the heavy metal leachate is below permissible limit of discharge which is according to Indian Standard [IS:2490 (Part-I), 1981](Chand et. al., 2016).
In India phosphorus fertilizers are often used in excess in farming, leading to accumulation in top soil. Long term use of phosphorus in soil leads to leaching from soil, since phosphorus is relatively immobile (Rashmi et. al., 2016).
In India, fly ash and slag leachant pollution are causing great environmental damage. The generation of these pollutants is in huge quantity, from iron and steel plants and thermal power plants (Tiwari et. al., 2015). A simulation of various leaching method was done by Tiwari et. al., 2015 to find the presence of heavy metal and impact of disposal of these pollutants. The primary consideration while choosing the suitable method are age of waste disposal, chemical and physical properties of pollutants, climatic condition of the area of disposal and the source composition. For this study, three leaching tests were compared; USEP, TCLP and ASTM D after screening from many other leaching tests.
The International Standards provide guidance for leaching testing. Some of them are:
It provide guideline for the suitable use of leaching tests on soil, determining leaching according to impact assessment or for comparing. The information includes:
It provides guidelines for the choice and implication of methods enhance the characteristics of contaminated soil. It does suggests boundary conditions and methods to be applied and provide minimum development requirements of the method. The compound which are considered as contaminants under this standard are metalloids, metal and organic compounds. This standard is applicable for pedological process and metallurgic process.
This standard specifies a test which provides information on soil leaching within experimental conditions, mainly for a liquid to solid ration of 10 litre per kilogram of dry matter. It is useful for soil with particle size less than or equal to 4 mm.
This standard was developed to analyse and measure the release of organic and inorganic elements from soil and the toxic effects of eluates on environment of micro-organism, flora and fauna. However, this test is not preferable for elements that shows volatile behaviour in ambient situation. The procedure of this test generates eluates which have distinguish chemical, ecotoxicological and physical standards.
This test is for routine testing and control purpose and therefore, cannot be unaccompanied used to explain all of the leaching properties of the soil and soil materials.
This standard provides guidelines regarding classification of soils with respect to its functional habitat, retaining and use. This standard belongs to the family of other two standards ISO 15799 and ISO 19204. It would be appropriate to apply this standard along with the combination of the other two standard. It shows direction to choose and evaluate the test which is useful for recognise ecotoxicological aspects of soil and soil materials. It recommend strategy of test while considering the safety of surface and ground water and conservation of functional habitat of the soil.
Yang, N., Damgaard, A., Kjeldsen, P., Shao, L. M., & He, P. J. (2015). Quantification of regional leachate variance from municipal solid waste landfills in China. Waste management, 46, 362-372.
ISO 18772:2008 Soil quality — Guidance on leaching procedures for subsequent chemical and ecotoxicological testing of soils and soil materials. (2008). Organization Internationale de Normalisation. Retrieved from https://www.iso.org/standard/38867.html
ISO 17402:2008 Soil quality — Requirements and guidance for the selection and application of methods for the assessment of bioavailability of contaminants in soil and soil materials. (2008). Organization Internationale de Normalisation. Retrieved from https://www.iso.org/standard/38349.html
ISO/TS 21268-2:2007 Soil quality — Leaching procedures for subsequent chemical and ecotoxicological testing of soil and soil materials — Part 2: Batch test using a liquid to solid ratio of 10 l/kg dry matter. (2007). Organization Internationale de Normalisation. Retrieved from https://www.iso.org/standard/44146.html
ISO 17616:2019 Soil quality — Guidance on the choice and evaluation of bioassays for ecotoxicological characterization of soils and soil materials. (2019). Organization Internationale de Normalisation. Retrieved from https://www.iso.org/standard/73592.html
Hao, Y., Wu, S., Pan, Y., Li, Q., Zhou, J., Xu, Y., & Qian, G. (2016). Characterization and leaching toxicities of mercury in flue gas desulfurization gypsum from coal-fired power plants in China. Fuel, 177, 157–163.doi:10.1016/j.fuel.2016.02.091
Tiwari, M. K., Bajpai, S., Dewangan, U. K., & Tamrakar, R. K. (2015). Suitability of leaching test methods for fly ash and slag: A review. Journal of Radiation Research and Applied Sciences, 8(4), 523–537. doi:10.1016/j.jrras.2015.06.003
Chand, S., Paul, B., & Kumar, M. (2016). Short-term leaching study of heavy metals from LD slag of important steel industries in Eastern India. Journal of Material Cycles and Waste Management, 19(2), 851–862.doi:10.1007/s10163-016-0486-z
Dorman, F. L., & Dawes, P. (2012). Column Technology: Open Tubular. Gas Chromatography, 79.
Malenga, E.N., Mulaba-Bafubiandi, A.F., Nheta, W., 2015. Alkaline leaching of nickel bearing ammonium jarosite precipitate using KOH, NaOH and NH4OH in the presence of EDTA and Na2S. Hydrometallurgy 155, 69-78
Rashmi, I., Biswas, A. K., Parama, V. R. R., Athifa, M., & Ramteke, L. (2016). Soil Testing Indices for Phosphorus Leaching in Selected Vertisol and Inceptisol of India. Proceedings of the National Academy of Sciences, India Section B: Biological Sciences, 88(3), 867–874. Doi: 10.1007/s40011-016-0823-y
Yin, S., Wang, L., Wu, A., Free, M. L., & Kabwe, E. (2018). Enhancement of copper recovery by acid leaching of high-mud copper oxides: A case study at Yangla Copper Mine, China. Journal of Cleaner Production, 202, 321–331.doi:10.1016/j.jclepro.2018.08.122
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