No abstract

The capacity of the biomass for single metal ions (around 1 mmol/g) was increased to 1.3 mmol/g in competitive adsorption, Pb(II) showing the highest Langmuir intensity constant. Considering its extremely high abundance and low cost, C. barbata may be potentially important in metal ion removal from contaminated water and industrial effluents.

Two laboratory-scale separation processes have been developed for the recovery of copper (II) from acidic and cyanide-containing alkaline wastewater of electroplating industries. Acidic bath wastes were treated with Dowex 50X8, a strongly acidic cation-exchange resin, and the retained copper was eluted with H 2 SO 4 . The cyanide-containing alkaline bath waste was first oxidized with excessive hypochlorite, then neutralized, and recovered by the use of Amberlite IRC-718 chelating resin. Copper was eluted with H 2 SO 4 .The two different valencies of chromium have been recovered from electroplating-industry wastewater by different separation processes: The predominant valency, Cr(VI), was retained on a strongly basic Dowex 1X8 resin and eluted with a NaCl and ORDER REPRINTS NaOH solution. Alternatively, Cr(III), either existing originally in electroplating-industry waste-rinse mixtures or converted from Cr(VI) by reduction with Na 2 SO 3 , could be recovered by a weakly acidic Amberlite IRC-50 resin and eluted with a solution containing H 2 O 2 and NaOH. Where plating industry wastes contain high levels of organic contamination, Cr(VI) would be naturally reduced to Cr(III) upon acidification, and it may be more economical to recover all chromium as Cr(III).

The biosorption mechanism of divalent Ni(II), Cd(II), and Pb(II) ions onto calcium treated Entemorpha linza was investigated as a function of pH, contact time, biomass dose, and temperature. The experimental data were evaluated by Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. The uptake capacity of the tested metal ions was markedly influenced by pH in the range of 2–3.5 and maximum rates were observed at pH 5–5.5. The kinetics of the metal ions adsorption were rather rapid, with 90% of adsorption occurring within 10 min. In addition to batch sorption tests, the functional groups on the cell wall matrix of the biomass were revealed by potentiometric titration data and Fourier transform infrared analysis. The relative contribution of the chemical groups involved in metal biosorption such as carboxyl, amino, sulfonate was evaluated to characterize their binding mechanisms using these instrumental techniques. The density of strong and weak acidic functional groups in the biomass was found to be 0.25 and 0.95 mmol g−1 biomass, respectively. In conclusion, the present work showed that the marine algae E. linza could be used as a potentially cost‐effective biosorbent for the treatment of complex wastewater containing heavy metals.

A XAD-shellac sorbent, synthesized by the impregnation of the natural polymer shellac (purified product of the hardened resinous secretion of the lac insect Kerria lacca) on Amberlite XAD-16 copolymer backbone, has been developed for the separation of Cr(III) from Cr(VI), and preconcentration of Cr(III) from synthetic solutions and real samples. The preconcentration factor for Cr(III) was 75. All chromium determinations were made using the diphenyl carbazide spectrophotometric method after oxidizing Cr to chromate(VI) where necessary, and simultaneously with flame-AAS for confirmation. The dynamic breakthrough and batch capacities of this sorbent for Cr(III) were 0.3 and 0.9 mg g À1 , respectively, indicating that the ion-exchange mechanism was prevalent in the dynamic mode, whereas in the batch mode, the surface sites were also capable of exerting their chelating effects. When XAD-shellac was thoroughly washed with ammonium acetate solution prior to use in chromium speciation, the cationic (RH þ ) surface sites were probably neutralized to yield free acetic acid, and the resulting resin did not retain CrO 2À 4 : Thus, complete separation and speciation of Cr(III) from CrO 2À 4 was possible using this sorbent. The shellac-coated sorbent decomposed in alkaline solution (i.e. over pH 7.5), and therefore the retained Cr(III) was eluted with dilute (0.025-0.050 M) HCl. Thus, Cr(III) in admixture with Cr(VI) could be separated and recovered, without interference from the hexavalent state. XAD-shellac was not successful for Cr preconcentration from seawater, but was efficiently used for synthetic and real electroplating wastewater and CRMs such as SO-2 soil, San Joaquin soil, BCR 145 R sewage sludge, with a recovery ratio for Cr(III)/Cr(VI) extending up to 98%.