CONICET | Buscador de Institutos y Recursos Humanos

Use of agricultural and biomaterials wastes in biosorption of chromium Luis F. Sala, Patricia Blanes (Becaria ANCEFN), Ma. Inés Frascaroli, Jousy García, Silvia I. García, Juan Carlos González, Ma. Florencia Mangiameli IQUIR, CONICET, FCByF, UNR, Suipacha 531, Rosario, Argentina, sala@iquir-conicet.gov.ar The toxic and genotoxic nature of the CrVI ion was established a long time ago. Industrial process of prodution release a relatively large quantity of Cr into the atmosphere, earth, lakes and rivers. In soil and water the less toxic CrIII ion can be oxidized to carcinogenic and mutagenic chromium, CrVI. It is assumed that the redution of CrVI to CrIII takes place in living organisms. Reduction of Cr concentration from effluents to a permissible limit before discharging them into aquatic ecosystem is important for human health and environment. Adsorption is an effective method for removing Cr, solving the sludge disposal problem. Such process is economically viable, especially if low-cost adsorbents are used. Agricultural and biomaterials wastes studied for the adsorption efficiency include pectic-rich (grapefruit and lemon peel (LP)) and lignocelullosic biomaterials (rice husk, soya husk (SH)). The amounts of adsorbed Cr on biomaterials, depends on diferentens conditions, like: mass of the adsorbent (m), acidity of the medium and contact time between the adsorbate and adsorbent. For treatment of data, the Design Expert Software release 6.0.10 was employed. CrVI was determined at 540 nm with 1,5-diphenylcarbazide reaction and CrIII, was determined after oxidating it to CrVI using saturated solution K2S2O8 and AgNO3 as catalyst. The amount of Cr adsorbed by biomaterials treated with CrIII was calculated from the difference between the initial chromium concentration of the control solutions and the final total Cr concentration in the respective supernatant solutions. For CrIII removal from aqueous solutions, the best conditions for CrIII uptake were LP: m=2.34 g, SH: m=5.1 g, at pH=4.5. To characterize the main mechanism of CrVI removal, it is very important to verify the oxidation state of the chromium bound to the biomaterial. If this state is only trivalent, it can be concluded that CrVI was completely reduced to CrIII by the biomaterial. If intermediate chromium oxidation states are detected on the surface of the biomaterial, it can be concluded that CrVI was first adsorbed onto the surface and then reduced by functional groups in the biomaterial surface. CrIII (d3) and CrV (d1) contain unpaired electrons; and are detected for electron paramagnetic resonance (EPR). For all materials intermediaries of CrV were detected, e.g. EPR spectra of LP exhibit a sharp signal at giso=1.9785, characteristic of CrV. The final Cr specie was CrIII as can be seen in the EPR spectra. Key boards: remediation, chromium, biomaterial.