José Carlos Casagrande

Nickel adsorption by soils in relation to pH, organic matter, and iron oxides

Ha poucas informacoes disponiveis na literatura quanto a adsorcao de niquel em solos do Brasil. O objetivo deste trabalho foi determinar a influencia do pH, da materia orgânica, e dos oxidos de ferro na adsorcao de niquel em amostras da camada superficial (0 a 0,20 m) de um Latossolo Vermelho acriferrico tipico (LVwf), textura argilosa, um Latossolo Amarelo acrico tipico (LAw), textura argilo-arenosa e um Nitossolo Vermelho eutroferrico (NVef), textura muito argilosa. Foram utilizadas amostras de solo natural, de solo sem materia orgânica (MO), e de solo sem materia orgânica e sem oxidos de ferro, para fazer envelopes de adsorcao (2,0 g de solo + 20 mL de solucao contendo 5 mg L-1 de Ni em CaCl2 0,01 mol L-1, variando o pH de 3,5 a 7,5). A adsorcao de niquel diminuiu com a eliminacao da MO; a eliminacao de MO e de oxidos de Fe so provocou diminuicao na media de adsorcao no LVwf; o pH foi o principal fator de variacao na adsorcao de niquel e, com a eliminacao da MO e dos oxidos de Fe, os picos de adsorcao foram atingidos a valores mais elevados de pH.

COPPER ADSORPTION IN OXIDIC SOILS AFTER REMOVAL OF ORGANIC MATTER AND IRON OXIDES

Copper (Cu), despite being an essential micronutrient, may be toxic whenever it occurs in the soil solution at high concentrations. Chemical reactions that control copper availability in the soil–plant system are complex. Copper can be found in both organic and inorganic soil fractions. This work studied Cu adsorption into surface (0–0.2 m) and subsurface (in the B2 horizon) samples from three Brazilian soils, namely a heavy clayey-textured anionic Rhodic Acrudox (RA), a medium-textured anionic Xanthic Acrudox (XA) and a heavy clayey-textured Rhodic Hapludalf (RH), before and after the removal of organic matter (OM) and iron oxides. pH values were adjusted to 5 with either HNO3 or Ca(OH)2. In natural samples, when OM was not removed, Cu adsorption did not differ statistically among the surface samples. Cu adsorption, however, was significantly lower in the subsurface samples of XA and RA. Removal of OM influenced Cu retention only in XA and RA surface samples. In the subsoil, which had low OM contents, elimination of OM did not significantly affect adsorption. In RH, the amounts of Cu adsorbed were not significantly affected by OM removal, and the mineral fraction, basically constituted of kaolinite, contributed almost entirely to the adsorption reactions. When soil pH was below the zero point of salt effect (ZPSE), iron oxides removal increased Cu retention, likely due to a reduction in repulsion between the positively charged surface and the metal. For pH values above ZPSE, oxides effectively contributed for Cu adsorption, since their removal was followed by a decrease in Cu retention.

Copper adsorption as a function of solution parameters of variable charge soils

Effects of pH and ionic strength (I) on copper (Cu) adsorption and the driving force of the reaction in variable charge soils were evaluated from batch studies. Experimental results of Cu adsorption fitted Langmuir model. According to adsorption isotherms, Cu affinity (KL) was greater in the subsoil (0.061-0.468 L kg-1) than in the topsoil samples (0.169-0.359 L kg-1). Maximum adsorption (Adsmax) ranged from 1114-2422 mg kg-1 (topsoil) to 1002-1334 mg kg-1 (subsoil). Strong dependence of Cu adsorption on the pH was observed in subsoil samples. Adsorption edges showed sharply increase of Cu adsorption (20-90%) in the 4.0-5.0 pH range. Copper adsorption changed with increase in I and indicated different metal retention mechanisms (outer- and inner-spheres). Adsorption reaction was favorable and spontaneous, as indicated by negative values of the free energy variation (ΔG) and the separation factor KR < 1. Soil-solution interface and Cu adsorption were also thermodynamically described by a theoretical approach.

Zinc adsorption in highly weathered soils

The objective of this work was to assess the effects of pH and ionic strength upon zinc adsorption, in three highly weathered variable charge soils. Adsorption isotherms were elaborated from batch adsorption experiments, with increasing Zn concentrations (0-80 mg L -1 ), and adsorption envelopes were constructed through soil samples reactions with 0.01, 0.1 and 1 mol L -1 Ca(NO3)2 solutions containing 5 mg L -1 of Zn, with an increasing pH value from 3 to 8. Driving force of reaction was quantified by Gibbs free energy and separation factor. Isotherms were C-, H- and L-type and experimental results were fitted to nonlinear Langmuir model. Maximum adsorption ranged from 59-810 mg kg -1 , and Zn affinity was greater in subsoil (0.13-0.81 L kg -1 ) than in the topsoil samples (0.01-0.34 L kg -1 ). Zinc adsorption was favorable and spontaneous, and showed sharply increase (20-90%) in the 4-6 pH range. No effect of ionic strength was observed at pH values below 5, because specific adsorption mechanisms predominated in the 3-5 pH range. Above pH 5, and in subsoil samples, Zn was adsorbed by electrostatic mechanisms, since ionic strength effect was observed. Despite depth and ionic strength effects, Zn adsorption depends mainly on the pH.

Parâmetros Termodinâmicos da Reação de Adsorção de Boro em Solos Tropicais altamente Intemperizados

The driving force of boron adsorption on some tropical soils was evaluated by means of thermodynamic parameters. The batch method was employed, and the reaction was monitored at different pH values. The Langmuir equation successfully fitted the experimental results and provided reasonable isotherm parameters. Boron adsorption increased as a function of the pH of the soil solution and the concentration of added boron. The reaction was favorable and proceeded spontaneously, being strongly exoergic, as indicated by a negative free energy (DG) and a separation factor (KR) < 1. The boron adsorption phenomenon and the soil-solution interface were thermodinamically described using a theoretical model.

Effects of pH and Ionic Strength on Zinc Sorption by a Variable Charge Soil

Abstract Ionic strength and pH influence the adsorption of cations due to the variation of the electric charge in soils rich in iron (Fe) and aluminum (Al) oxides and hydroxides. The objective of this study was to investigate the influence of pH and ionic strength on zinc (Zn) sorption in a highly weathered Brazilian soil. The equations of Langmuir and Freundlich were adjusted to describe the adsorption. Zinc adsorption increased with the elevation of the pH and with the decrease of the ionic strength. The pH effect, however, surpassed the effect of the ionic strength. The largest variation of adsorption with pH suggests the presence of high-affinity adsorption sites. Langmuir and Freundlich equations were well fitted to zinc adsorption at all pH and ionic strength values. At all ionic strength and pH values, maximum adsorption in the surface layer, with negative balance of charge, was higher than in the subsoil, wherein the zero point of salt effect was higher than the soil pH in CaCl2.

Effect of Ionic Strength and pH on Cadmium Adsorption by Brazilian Variable‐Charge Soils

Batch adsorption experiments were conducted to assess the effects of pH and ionic strength (I) on cadmium (Cd) adsorption by two Brazilian Oxisols. Adsorption envelopes were constructed through soil sample reactions with 0.01, 0.1, and 1 mol L−1 calcium nitrate [Ca(NO3)2] solutions containing 5 mg L−1 of Cd, with an increasing pH value from 3 to 8. The adsorption increased drastically with increasing pH, varying from 20 to 90% in a narrow pH range (4–6 in topsoil and 5–6 in subsoil). Gibbs energy (ΔG) for Cd adsorption was negative, and the phenomenon became more thermodynamically spontaneous with an increase in pH. Under the standard 0.01 mol L−1 I and at pH close to natural, the ΔG values ranged from −796 to −3427 J mol−1. No effect of I was observed on the ΔG values for Cd adsorption at pH values less than 6. At values greater than pH 6, sharp changes in the Cd adsorption pattern were observed on subsoil samples. The only soil attribute significantly correlated with the spontaneity of Cd adsorption was the effective cation exchange capacity, ECEC (r = 0.97; p < 0.1).

Isotermas de langmuir e de freundlich na descrição da adsorção de boro em solos altamente intemperizados

The objective of this study was to evaluate Langmuir and Freundlich isotherms applied to boron adsorption in highly weathered Brazilian soils. Surface (0-0.2 m) and subsurface (B horizon) samples were taken from a Rhodic Hapludox (Dusky red latosol = LR); Typic Hapludox (Dark-red latosol = LE), and one Arenic Paleudalf (Red-yellow podzolic _ PV). In order to quantify the adsorbed boron, 4 g of oven-dried soil were stired in polyethylene tubes, for 24 h, with 20 mL of a CaCl2 (0.01 mol.L-1) solution containing different quantities of boron (0, 1, 2, 4, 8 and 16 mg.mL-1). Langmuir and Freundlich constants were estimated by nonlinear regressions. Boron adsorption was well described by both Langmuir and Freundlich models over the studied range of boron concentrations (0 to 16 mg.mL-1) for all three soils. Adsorption maximum decreased from the LR samples (around 14 mg.g-1) to the PV subsurface sample (7 mg.g-1) and then to the surface PV horizon and LE samples (less than 6 mg.g-1). The Langmuir model exhibited lower sum of deviations in relation to the PV and the LE. The opposite occurred for the LR, where the sum of deviations was high for the Freundlich model.

Copper desorption in a soil with variable charge

A adsorcao de metais pesados aos solos e mais estudada do que sua dessorcao. No entanto, o processo de dessorcao esta diretamente relacionado a disponibilidade dos elementos as plantas. A dessorcao de cobre em amostras superficiais (0-0,2 m) e subsuperficiais (1,0-1,2 m) de um Latossolo Vermelho acriferrico foi estudada em dois valores de pH (4,5 e 7,5). Foram adicionados ate 400 mg kg-1 de Cu em amostras incubadas por 4 e 12 semanas, tendo o CaCl2 como eletrolito suporte nas concentracoes de 0,01 e 0,001 mol L-1. No pH mais elevado (7,5), em todos os periodos de incubacao, as amostras adsorveram praticamente todo o cobre adicionado, indicando que o tempo de 24 h de agitacao para se atingir o equilibrio foi suficiente para atingir a adsorcao maxima. A adsorcao de Cu variou com o tempo de incubacao do elemento com o solo. No pH mais baixo (4,5), a adsorcao foi bem menor apos 24 h de incubacao. Apos 4 e 12 semanas, as adsorcoes foram elevadas e semelhantes para todas as amostras, independentemente da profundidade e do pH. Para todas as doses estudadas, o efeito do tempo de incubacao na adsorcao de cobre pelo solo sobrepujou o efeito do pH. O fenomeno de histerese foi expressivo, sugerindo que o Cu forma ligacoes de alta energia com os coloides do solo. O cloreto de calcio nao foi eficiente para dessorver cobre nativo do solo.

Influência do pH na sorção de imazaquin em um Latossolo Vermelho Acriférrico

Imazaquin herbicide is an organic molecule presenting ionizable functional groups, with its sorption depending on soil pH and electrical charges. In this research, sorption of imazaquin was evaluated on an Anionic Acrudox at different soil depths and pH values. Radiolabelled (14C) molecules were employed to study imazaquin sorption, which was estimated by the difference between applied concentration and that remaining in solution. The sorption data were fitted to Freundlich equation to determine the sorption coefficient values (Kf), which were, overall, low in the studied soil. At both soil depths, sorption decreased as pH increased. However, at a similar pH value, sorption was higher on the subsurface than on the surface sample, probably due to the positive charges resulting from the low organic matter and high Al and Fe oxide contents. When the soil surface charges were positive it was not possible to predict imazaquin sorption only from molecule speciation and its hydrophobic partition into soil organic fractions.