Selective recovery of precious metals by persimmon waste chemically modified with dimethylamine.
ABSTRACT Persimmon waste was chemically modified with dimethylamine (DMA) to obtain a tertiary-amine-type gel, named DMA persimmon waste gel (DMA-PW). It was found to be effective for the adsorption of Au(III), Pd(II), and Pt(IV) in hydrochloric acid medium. In contrast, base metals such as Cu(II), Zn(II), Fe(III), and Ni(II) were not practically adsorbed. The formation of ion pairs of the metal chloro complex anions with the protonated adsorption gels was proposed as the main adsorption process. The gel exhibited selectivity only for precious metals with a remarkably high capacity for Au(III), i.e., 5.63 mol/kg dry gel and comparable capacities, i.e., 0.42 and 0.28 mol/kg for Pd(II) and Pt(IV), respectively. According to the kinetic and electrochemical studies, the adsorption rate of Au(III) was greatly enhanced by the chemical modification. Also, its excellent adsorption characteristics for the precious metals were confirmed by adsorption and elution tests using a column packed with the DMA-PW gel.
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ABSTRACT: The objectives of this study are to identify the various techniques used for treating electronic waste (e-waste) at material recovery facilities (MRFs) in the state of California and to investigate the costs and revenue drivers for these techniques. The economics of a representative e-waste MRF are evaluated by using technical cost modeling (TCM). MRFs are a critical element in the infrastructure being developed within the e-waste recycling industry. At an MRF, collected e-waste can become marketable output products including resalable systems/components and recyclable materials such as plastics, metals, and glass. TCM has two main constituents, inputs and outputs. Inputs are process-related and economic variables, which are directly specified in each model. Inputs can be divided into two parts: inputs for cost estimation and for revenue estimation. Outputs are the results of modeling and consist of costs and revenues, distributed by unit operation, cost element, and revenue source. The results of the present analysis indicate that the largest cost driver for the operation of the defined California e-waste MRF is the materials cost (37% of total cost), which includes the cost to outsource the recycling of the cathode ray tubes (CRTs) (dollar 0.33/kg); the second largest cost driver is labor cost (28% of total cost without accounting for overhead). The other cost drivers are transportation, building, and equipment costs. The most costly unit operation is cathode ray tube glass recycling, and the next are sorting, collecting, and dismantling. The largest revenue source is the fee charged to the customer; metal recovery is the second largest revenue source.Environmental Science and Technology 04/2006; 40(5):1672-80. · 5.26 Impact Factor
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ABSTRACT: This study is on the kinetics and thermodynamics of the adsorption of Pb(2+) onto phosphate-modified and unmodified kaolinite clay obtained from Ubulu-Ukwu in Delta State of Nigeria. Increasing initial Pb(2+) concentration increased the rate of Pb(2+) adsorbed with increase in initial Pb(2+) concentration from 300 to 1000 mg/L. Increasing Pb(2+) concentration also increased the initial sorption rate h, from 1.404 to 13.11 mgg(-1)min(-1) for phosphate-modified kaolinite clay and 1.04-3.48 for unmodified kaolinite clay as Pb(2+) concentration. Increase in temperature was found to increase the initial sorption rate of Pb(2+) adsorption onto phosphate-modified adsorbent from 3.940 to 8.85 and 2.55 to 4.16 mgg(-1)min(-1) for the unmodified adsorbent. The overall sorption rate k, increased only slightly from 5.1x10(-2) to 9.7x10(-2)gmg(-1)min(-1) for phosphate-modified adsorbent, 3.8x10(-2) to 5.4x10(-2)gmg(-1)min(-1) for unmodified adsorbent. The adsorption reaction on both adsorbents was found to be chemically activated reaction and endothermic with energy of activation, E, at 500mg/L of Pb(2+) in solution as 19 and 10.68 kJmol(-1) for phosphate-modified and unmodified adsorbents, respectively. The positive values of both DeltaH degrees and DeltaS degrees obtained suggest an endothermic reaction and in increase in randomness at the solid-liquid interface during the adsorption of Pb(2+) onto the adsorbents. DeltaG degrees values obtained were all negative indicating a spontaneous adsorption process. The presence of Cd(2+) decreased both initial sorption rate and the amount of Pb(2+) adsorbed on phosphate-modified and unmodified adsorbents at equilibrium. The adsorption process follows a pseudo-second-order reaction scheme.Journal of Hazardous Materials 07/2007; 144(1-2):386-95. · 3.93 Impact Factor
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ABSTRACT: We have proposed a new recovery system of hexavalent chromium Cr(VI) that is of great toxicity utilizing condensed-tannin gels derived from a natural polymer with many polyhydroxyphenyl groups. The adsorption mechanism of Cr(VI) to the tannin molecules was clarified. The adsorption mechanism consists of four reaction steps; the esterification of chromate with tannin molecules, the reduction of Cr(VI) to trivalent chromium Cr(III), the formation of carboxyl group by the oxidation of tannin molecules and the ion exchange of the reduced Cr(III) with the carboxyl and hydroxyl groups. It was found in this recovery system that a large amount of proton was consumed accompanied with the reduction of Cr(VI) so that the acidic solution containing Cr(VI) was transferred automatically to neutral one by choosing an appropriate initial pH. The carboxyl group which was created by the oxidation of tannin molecules parallel to the reduction of Cr(VI) to Cr(III) contributed to an increase in the ion-exchange sites of the reduced Cr(III). The maximum adsorption capacity of Cr(VI) reached 287 mg Cr/g dry tannin gel under the conditions of 0.77 water content of tannin gel and the initial pH = 2. This adsorption capacity was five to ten times higher than that obtained by the ion exchange between ordinary Cr(III) and tannin molecules for the tannin gels prepared under similar conditions. The system proposed here will provide an important information on a zero-emission-oriented process because it has such advantages as higher adsorption capacity of chromium and lower volume of secondary wastes compared with conventional process.Water Research 03/2001; 35(2):496-500. · 4.66 Impact Factor