Otávio Antonio de Camargo

Sílica solúvel em solos

Determinou-se a silica soluvel nos horizontes superficial e B2 de 44 perfis de solos do Estado de Sao Paulo. A extracao da silica com solucao 0,0025M de cloreto de calcio evitou a dispersao dos solos e forneceu resultados em media apenas 8% menores do que a silica soluvel em agua. Os resultados variaram de 2,2 a 92,2 ppm de SiO2. Verificou-se que, para solos com teores semelhantes de argila, os teores de silica soluvel foram maiores para solos com horizonte B textural, quando comparados com solos de horizonte B latossolico. Dentro dos agrupamentos de solos com horizonte B textural e horizonte B latossolico, os teores de silica soluvel foram maiores para os solos mais argilosos. Nao foi observada relacao entre silica soluvel e o pH dos solos.

Atributos químicos e produção de milho em um latossolo vermelho eutroférrico tratado com lodo de esgoto

A utilizacao de lodo de esgoto como fertilizante orgânico ou condicionador do solo, tem-se tornado cada vez mais atraente, pelos altos custos e impactos ambientais relacionados com os demais metodos de disposicao, pela presenca de nutrientes vegetais e materia orgânica no lodo e pela necessidade de reducao de custos na agricultura. No entanto, em sua composicao, pode conter metais pesados, microrganismos patogenicos e compostos orgânicos toxicos. Visando estudar os efeitos da aplicacao de lodo de esgoto em areas agricolas, foi realizado um experimento, com duracao de dois anos agricolas, para determinar alteracoes em propriedades quimicas do solo, principalmente sobre os teores de P, Cu, Ni e Zn em um Latossolo Vermelho eutroferrico, de textura argilosa, cultivado com milho. O experimento consistiu na aplicacao de lodo de esgoto em duas doses comparadas a uma testemunha com adubacao quimica. Para analise de rotina das propriedades quimicas e do teor de Ni do solo, foram coletadas amostras nas profundidades de 0-0,05; 0,05-0,10 e 0,10-0,20 m apos a colheita do milho no primeiro e no segundo ano. Foi feita, tambem, uma extracao sequencial de P em amostras da camada de 0-0,05 m, na seguinte ordem: CaCl2 (P biologicamente mais disponivel); NaHCO3 (P disponivel); NaOH (P ligado aos oxidos de Fe e Al); HCl (P ligado a Ca) e digestao nitrico-perclorica (P residual). A producao do milho foi maior nos tratamentos com aplicacao do lodo. Os teores disponiveis de P no solo onde foi aplicado lodo foram semelhantes aos do tratamento sem lodo e com adubo quimico. Entretanto, a aplicacao do lodo aumentou as fracoes labeis e moderadamente labeis do P na camada superficial. Os dados indicaram, por outro lado, aumento dos teores de Cu, Ni e Zn no solo e de Zn na planta. Dessa forma, faz-se necessario constante monitoramento do solo onde o lodo de esgoto e aplicado para o controle adequado dos teores de metais.

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.

Sorption and desorption of cadmium and zinc in two tropical soils amended with sugarcane-straw-derived biochar

PurposeBiochars may enhance the retention capacity of metals in soils, especially in highly weathered tropical soil whose low cation exchange capacity renders heavy metals mobile, and thus be able to leach from soils. We evaluated the effect of sugarcane-straw-derived biochar on sorption and desorption of Cd(II) and Zn(II) in two tropical soils in particular to distinguish primary and secondary mechanisms of metal retention.Material and methodsTo test the efficiency of biochar to retain heavy metals, sugarcane-straw-derived biochar was mixed with a clayey Oxisol and an Entisol both from the state of Sao Paulo, Brazil, in batch testing to obtain sorption-desorption isotherms of Cd(II) and Zn(II) and measure the release/displacement of cations (Ca2+ and Mg2+) or precipitation with phosphate during the sorption process.Results and discussionBiochar increased the sorption (including adsorption and precipitation) of both metals in both soils but that most sorption reactions were reversible under buffer acidic conditions, due to dissolution of precipitates in low pH values (<4.9). Exchange of Cd or Zn with Ca and Mg from the biochar was found to play a minor role on the retention mechanism, whereas surface precipitation (mainly in the Entisol) of the metals (e.g. with phosphate) was likely to be the main sorption mechanism.ConclusionsApplication of sugarcane-straw-derived biochar to heavy-metal-contaminated tropical soils seems justified because of its sorptive capacity for Cd and Zn. However, binding reactions on surfaces were reversible, mainly for Cd(II), resulting in the likelihood that repeat applications of biochar would be required to maintain reduced soil solution concentrations of Cd and Zn over time, thus avoiding phytotoxicity and associated environmental risks.

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.

Boron adsorption in soils from the State of São Paulo, Brazil

Boron adsorption was studied in five representative soils (Rhodic Hapludox, Arenic Paleudalf and three Typic Hapludox) from the State of Sao Paulo, Brazil. Adsorption was higher in the clayey Oxisols, followed by the Alfisol and the coarser Oxisols. Calcium carbonate promoted an increase in the amount of adsorbed boron in all soils, with the most pronounced effect in the coarser-textured Oxisols. High correlation coefficients were found between adsorbed boron and clay and amorphous aluminum oxide contents and specific surface area (r = 0.79, 0.76 and 0.73, respectively, p < 0.01). Clay content, free aluminum oxide, and hot CaCl2 (0.01 mol L-1)-extracted boron explained 93% of the variation of adsorbed boron. Langmuir and Freundlich isotherms fitted well to the adsorbed data, and highest values for maximum boron adsorption were found in clayey soils, which were significantly correlated with contents of total, free and amorphous iron and aluminum oxides, as well with the physical attributes. Ninety four percent of the variation in the maximum adsorption could be related to the free iron content.

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.

Crescimento e acúmulo de crômio em alface cultivada em dois latossolos tratados com CrCl3 e resíduos de curtume

Tannery solid wastes and CrCl3 were applied to two Oxisols in a greenhouse pot experiment. Soils used were a Typic Eutrorthox (Dusky-Red Latosol - LRe) and Typic Haplorthox (Red-Yellow Latosol - LVA) of which the main difference was the manganese reducible content. The tannery wastes were sludge from the liming process with a total dry matter chromium content of 0.06 g kg-1 (LCL) and the primary sludge (LCR) with a total dry matter chromium content of 17 g kg-1. The sludges were applied at three different rates taking into account their total nitrogen content (10, 20 and 30 Mg ha-1 for the LCL and 19, 38 and 57 Mg ha-1 for the LCR, both at a dry weight basis). CrCl3 was applied at rates of 330, 660 and 990 kg ha-1 of chromium, equivalent to the rates of applied LCR sludge. Cr6+ was measured after 1, 6, 14, 28, 54 and 86 days of incubation. After the 56th day, a one month old lettuce seedling (Lactuca sativa L.) was planted and grown for 30 days. The Cr3+ oxidation was detected only at the CrCl3 treatment of the LRe soil, being the highest amount found after the first day of incubation (0.72 to 1.16% of the total applied Cr), decreasing afterwards to non detection limits in the 54th day. The application of both sludges increased the electrical conductivity (1.40 to 5.07 dS m-1) and the sodium adsorption rate (3.05 to 14.12). It affected lettuce development causing death of the plants at the highest rates. LCR and CrCl3 treatments increased the levels of chromium in the plant tops but not always proportionally with the increasing applied rates. Both ocurrences were more pronounced for the LVA soil. Under the conditions of the experiment, lettuce growth was limited primarily by salt than by chromium content.

Cargas elétricas estruturais e variáveis de solos tropicais altamente intemperizados

Highly weathered tropical soils present high amount of colloids with variable electrical charge. However, there are few references related to the quantification of such charges, mainly in soils with acric attributes, which represent one of the extremes in the weathering scale. In this study permanent and variable charges were determined in four Oxisols and compared to an Alfisol with predominantly permanent charge. Samples were investigated using the Cs+ adsorption method, which measures the structural permanent charge (so) and is based on the preference of Cs+ over Li+ in the siloxane surface sites and the lower selectivity of ionizable surface group for the cesium ion. The variable charge represented more than 50% of the total charge of the evaluated soil samples. Two of the four Oxisols with acric properties had a significant permanent structural charge, probably due to small quantities of aluminum hydroxy-interlayer vermiculite and chlorite. The amount of permanent structural charges presented by the Alfisol was five times higher as compared to the Oxisols, which may be attributed to their mineral composition differences. The cesium adsorption method was able to quantify significant amounts of structural charges even in soils with a low amount of 2:1 clay minerals.