Detoxification of E-waste polluted site using cashew nut shell-based activated

11 This study considered the potential use of activated carbon (AC) produced from 12 cashew nuts for remediation of electronic waste (E-waste) polluted soil sites at 13 Agbogbloshie, Accra, Ghana. The AC supplied by Climate-Environmental Research 14 and Technology (CLERET) Laboratory, one of the research and development (R&D) 15 umbrellas of Explore Scientific Innovations Ltd., Ghana. It was prepared by a two- 16 stage process involving wood-fired reactor for thermal pyrolysis at temperature 17 ranging from 800-1000 o C, followed with activation with oxidizing gas generated by 18 wood-fired steam boiler at 160 o C and 7.5 atm pressure for 30 minutes. The product 19 was characterized based on bulk density, particle size, iodine number, electrical 20 conductivity (EC), porosity, and pH. Three replicates of soil samples were scooped 21 from at a depth of 0-15 cm using a soil auger from two randomly selected sites. The 22 samples were digested with 10 ml of ternary solution (20 ml of HClO 4 ; 500 ml of 23 HNO 3 ; 50 ml of H 2 SO 4 ) on a hot plate at 90°C for 30 minutes to an hour and analyzed 24 for selected heavy metals (Pb, Fe, Cu, Cr and Cd) using Atomic Absorption Spectrophotometer (AAS). The cashew nut shell-based AC significantly removed the 26 heavy metal contents of the E-waste polluted soil with removal efficiency in the 27 order: Cd (100%) > Pb (93%) > Fe (87%) > Cu (87%) > Cr (76%) for granular and 28 Cd (100%) > Pb (98%) > Fe (96%) > Cu (94%) > Cr (87%) for powdered activated 29 carbons. The slopes of the linear graph of the adsorption isotherms of the tested 30 metals which is indicative of the quality of adsorption of the metals were in the order: 31 Pb (0.9754) > Fe (0.9093) > Cr (0.8799) > Cu (0.8176) > Cd (0.7511). These agro- 32 based waste materials therefore have great potential for effective detoxification of E- 33 waste polluted sites. 34


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There is an exponential growth in the demand for electrical and electronic equipment 39 (EEE) globally due to rapid population growth, changing lifestyle, taste and 40 preferences [1]. This growth coupled with the speedy obsolescence of EEE as a result 41 of consistent technological advancement, diminishing product lifetimes, lack of soil bioremediation is the high toxin levels of chemical contaminants to soil micro and 76 macro organisms including plants used in phytoremediation. This often limits 77 utilization of this approach for treating contaminated soils [11]. 78 An effective heavy metal removal technique is required in detoxification of detoxification potential of AC on contaminated soils has also been studied 85 significantly. AC can be developed from many sources, such as palm husks, coconut 86 shells and almond husk. The use of agricultural by-products to replace wood as the 87 carbon source helps in utilizing biomass residues in a proper and efficient way 88 thereby reducing ecological impacts. The increasing generation and demands for 89 proper disposal of agricultural waste make their use as AC a promising bioresource. 90 This study therefore investigates the potential of AC produced from cashew nuts for 91 remediation of soil from E-waste polluted sites.  reading to a maximum of 25 atmospheres. The activation temperature by the reactor 141 operated between 500-600 o C. The high pressure gradient established between the 142 steam boiler and the reactor, which expelled the steam from the former to the latter.

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The carbon was activated for 30 minutes, after which the activation pressure became 144 exhausted, dropping below one atmosphere. To be consistent with experimental 145 design and to ensure production quality, three replications were made for the two-146 stage process. For each replicate, 50 kg of the raw material were used. The pH was determined with the standard method ASTM 3838-80. The ASTM 162 standard determination of pH is based on chemical reactions between the constituents 163 of the AC and its non-carbonaceous constituents and the adsorbate containing fluid.

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Ten grams of the AC were weighed into a beaker and 50 ml of distilled water were added. The mixture was stirred for 10 minutes to ensure proper dissolution of the 166 sample, left for one hour for the suspended particles to settle and later filtered. The pH 167 meter was first calibrated with standard buffer solution of pH 4.0 and 7.0. The 168 electrode was then immersed into the solution and the pH and electrical conductivity 169 readings were taken and recorded. The temperature of the solution was also recorded.          The mean iodine number and filtration rate were 719.14 ± 19.43 mg/g and 0.11 ± 279 0.15, respectively. Percentage composition of the various particle sizes of the AC produced is presented in Fig.   285 2. The composition of particles by size was in the order: 1 mm > 300 µm > 225 µm > 125 µm        and Cd > Pb > Fe > Cu > Cr for PAC (Table 4). Comparatively, powdered AC recovered 384 higher metal concentrations from the soils and had better adsorption rates than granular AC.

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This can be attributed to the fact the PAC have greater surface areas due to their nature which 386 enhances adsorption of the metals considered.    Availability of data and materials 467 All data generated or analyzed during this study are kept by the corresponding author and 468 will be provided upon request.

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Competing interests 471 The authors declare they have no competing interests.