Residues from the processing of cassava roots (Manihot esculentaCrantz), or cassava peels, are evaluated as chemically modified adsorbents with H2O2, H2SO4, and NaOH, in the removal of metal ions Cd(II), Pb(II), and Cr(III) from contaminated water. Modified adsorbents were chemically characterized for their chemical composition andpHPZC(point of zero charge), while adsorption tests determined the best conditions of pH, adsorbent mass, and contact time between adsorbent and adsorbate in the process of removal of the metal ions. Isotherms obtained from the preliminary results were linearized by Langmuir’s and Freudlich’s models. The thermodynamic parameters, such asΔH,ΔG, andΔS, were also evaluated. The modifying solutions proposed were effective in the modification of adsorbents and resulted in high capacity sorption materials. Equilibrium time between adsorbent and adsorbate for the solutions contaminated with metals is about 40 minutes. The Langmuir model adjusted to most results, indicating monolayers adsorption of Cd(II), Pb(II), and Cr(III). The values obtained for LangmuirQmshow a higher adsorption capacity caused by chemical modifications, with values such as 19.54 mg Cd(II) per g of M. NaOH, 42.46 mg of Pb(II) per g of M. NaOH, and 43.97 mg of Cr(III) per g of M H2O2. Results showed that modified cassava peels are excellent adsorbent, renewable, high availability, and low-cost materials and a feasible alternative in the removal of metals in industries.

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The purpose of this study was to investigate the availability of the heavy metals cadmium (Cd), lead (Pb), and chromium (Cr) to soil and maize plants fertilized with different sources and doses of zinc (Zn) in a Rhodic Eutrudox soil. For that purpose, concentrations of Cd, Pb, and Cr were evaluated in leaf tissue and grains of maize plants and in 0-20 and 20-40 cm soil layers after fertilization with four doses of Zn from eight different sources of fertilizer. There was no accumulation of Cd, Pb, and Cr in maize grain and Cd and Cr in leaf tissue of the plants; nevertheless, there was accumulation of Pb in leaf tissue, showing its availability throughout different sources of Zn and consequent uptake by plants. Regarding the soil, it was observed that fertilizer from the different sources made Cd, Pb, and Cr available at increasing amounts proportional to increased Zn doses. Under experimental conditions, fertilization with Zn increased concentrations of heavy metals Cd, Pb and Cr in soil, further highlighting the importance of conducting more studies related to the application of mineral fertilizers for micronutrient supply and the availability of heavy metals.

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ABSTRACT. Current study employs solid residues from the processing industry of the cassava (Manihot esculenta Crantz) (bark, bagasse and bark + bagasse) as natural adsorbents for the removal of metal ions Cu(II) and Zn(II) from contaminated water. The first stage comprised surface morphological characterization (SEM), determination of functional groups (IR), point of zero charge and the composition of naturally existent minerals in the biomass. Further, tests were carried out to evaluate the sorption process by kinetic, equilibrium and thermodynamic studies. The adsorbents showed a surface with favorable adsorption characteristics, with adsorption sites possibly derived from lignin, cellulose and hemicellulose. The dynamic equilibrium time for adsorption was 60 min. Results followed pseudo-second-order, Langmuir and Dubinin-Radushkevich models, suggesting a chemisorption monolayer. The thermodynamic parameters suggested that the biosorption process of Cu and Zn was endothermic, spontaneous or independent according to conditions. Results showed that the studied materials were potential biosorbents in the decontamination of water contaminated by Cu(II) and Zn(II). Thus, the above practice complements the final stages of the cassava production chain of cassava, with a new disposal of solid residues from the cassava agroindustry activity.Keywords: Solid residue, biosorbent, decontamination, adsorption, water contamination, toxic metals.Remoção de Cu(II) e Zn(II) de águas com adsorventes naturais de resíduos da agroindústria da mandioca RESUMO. Este estudo propõe a utilização de resíduos sólidos da indústria de processamento de raízes de mandioca (Manihot esculenta Crantz) (cascas, bagaço e casca mistura + bagaço) como adsorventes naturais para a remoção de íons metálicos Cu (II) e Zn (II) de águas contaminadas. Em uma primeira fase foi realizada a caracterização morfológica superficial (MEV), determinação dos grupos funcionais (IR), ponto de carga zero e a composição de minerais naturalmente existentes na biomassa. Após esta etapa, foram realizados testes para avaliar o processo de sorção mediante estudos cinéticos, de equilíbrio e termodinâmica. Os adsorventes apresentam superfície com características de adsorção favoráveis, com sítios ativos possivelmente derivados da lignina, celulose e hemicelulose. O tempo de equilíbrio dinâmico do processo é de 60 min. Os resultados seguem aos modelos de pseudo-segunda ordem, Langmuir, DubininRadushkevich, sugerindo quimissorção em monocamada. Os parâmetros termodinâmicos sugerem que o processo de biossorção de Cu e Zn é endotérmico, podendo ser espontâneo dependendo das condições. Concluiu-se que os materiais estudados são potenciais biosorventes para a descontaminação de águas contaminados por Cu (II) e Zn (II). Assim, esta prática complementa os estágios finais da cadeia produtiva da mandioca, dando um novo destino para resíduos sólidos de atividade mandioca agroindústria.Palavras-chave: resíduo sólido, biossorvente, descontaminação, adsorção, contaminação de águas, metais ...

Abstract:The objective of this work was to evaluate the removal of Cu 2+ and Zn 2+ in water by means of the adsorption process using three biosorbents derived from jatropha biomass (bark, endosperm and endosperm + seed coat). The experiments were performed in batch and evaluated the effect of solution pH, adsorbent mass, contact time, different initial concentrations of the metals Cu 2+ and Zn 2+, and the temperature of the solution during the adsorptive process. By kinetics, the adsorption isotherms and thermodynamics the mechanisms that control the adsorptive process were evaluated. The optimal conditions for the realization of the adsorptive process for both metals were: solution pH of 5.0 and 8 g L -1 of adsorbent mass per volume of solution, with a contact time between adsorbent and adsorbate of 60 min. According to the Langmuir model, the maximum adsorption capacities for the bark, endosperm and endosperm + seed coat of Jatropha were, respectively, for Cu 2+ 11.541, 20.475 and 22.910

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