Maurício Paulo Ferreira Fontes

Mobility of heavy metals as related to soil chemical and mineralogical characteristics of Brazilian soils

In order to better understand the relationship between soil characteristics and mobility of some heavy metals, correlation studies were conducted in samples of unlimed and limed A, B and C horizons of three Brazilian soils, representative of the majority of the tropical soils. A number of chemical and mineralogical characteristics of one Oxisol and two Ultisols were related to the retardation factors (Rf) for zinc (Zn), cadmium (Cd), copper (Cu) and lead (Pb). The retardation factors, obtained in leaching column experiments, were used as an estimate of solute movement in the profile. Soil types and soil horizons were found to influence metal retardation factors which, in turn, correlated better with the chemical than the mineralogical soil characteristics. For the unlimed soil samples, the soil characteristics that significantly correlated with Zn-Rf and Cd-Rf were the sum of exchangeable bases (SB), and soil exchangeable (Ca-KCl) and non-exchangeable (Ca-HCl) calcium contents. These results showed the strong influence of the cation exchange phenomenon on the retention and mobility of these two metals. For Cu and Pb, not only SB, cation exchange capacity (CEC) and Ca-KCl and Ca-HCl but also the organic matter correlated well with the Rf, showing that complex or chelate formation may play an important role in the movement of these elements. The important soil chemical characteristics related to the retardation factors in the limed soil samples were SB for Cd, and Ca-HCl for Cu and Pb, suggesting that precipitation may also influence the mobility and retention of the latter two heavy metals in these soil samples. Soil pH influenced the heavy metals adsorption and movement as shown by the significant correlation with the retardation factors when the combined data for the unlimed and limed soil samples was considered.

Phosphate adsorption by clays from Brazilian Oxisols: relationships with specific surface area and mineralogy

Oxisols derived from clayey sediments, sandstone, mafic rocks and schist were sampled in the “Triangulo Mineiro” region, Minas Gerais State, Brazil, to study the relationship between the phosphate adsorption and mineralogy and specific surface area. The specific surface area of the iron oxides estimated from N2 adsorption by the soil clays before and after dithionite-citrate dissolution of the Fe-oxides ranged from 45 to 110 m2 g−1. Specific surface area of the iron oxides correlated to the goethite: goethite +hematite ratio (r = 0.694∗). Specific surface area estimated by differential X-ray analysis did not show good agreement with BET-N2 adsorption values. Phosphate adsorption maxima for the soil clays (< 2 μm) ranged from about 70 to 160 μmol P g−1 of clay. Stepwise regression analysis showed phosphate adsorption for the total clays to be primarily related to goethite, gibbsite, the sum of Fe plus Al oxides and also amorphous Al oxides. A mild treatment for concentrating the soil iron oxides showed small effect in the phosphate adsorption for most soils. It showed the importance of gibbsite and crystalline Fe-oxides in the adsorption, with goethite explaining most of the variation occurring in P adsorption after the treatment. Correlation studies showed the adsorption capacity per unit specific surface to be somewhat dependent on variations in the iron oxide mineralogy of the clay samples. Clay color showed good correlation to the goethites: (goethite + hematite) ratio in soils but no direct relationship between phosphate adsorption and clay color was detected.

Simultaneous competitive adsorption of heavy metals by the mineral matrix of tropical soils

Abstract Disposal of sewage sludge, composts and industrial wastes onto agricultural lands is commonly and increasingly used in Brazil, potentially adding multi-component heavy metal solutions. Soil organic matter was removed from representative Brazilian soils and the simultaneous competitive adsorption on the mineral matrix of Cr, Ni, Cu, Zn, Cd and Pb was determined. The competition affected the behavior of heavy metal cations in such a way that the soils adsorbed less Ni, Zn and Cd and more Cr, Cu and Pb with increasing total concentrations, regardless of the molar concentration applied. On the other hand, the occupancy of the adsorption complex by the heavy metals was proportional to the relative concentration applied. As the applied concentrations increased Cr, Cu and Pb adsorption increased, while Ni, Zn and Cd adsorption decreased. The maximum adsorption capacity for the heavy metal cations was calculated, with the soils differing markedly. Ultisol and Alfisol soils showed the highest maximum adsorption values, in the order of 50.76 and 64.52 mmol kg−1, whereas some Oxisols showed the lowest values, in the order of 23.92 and 30.86 mmol kg−1. The results suggest that the first two soil types are capable of receiving and holding higher heavy metal loadings compared to the Oxisols, which are more vulnerable to heavy metal contaminant inputs.

Competitive Adsorption of Zinc, Cadmium, Copper, and Lead in Three Highly- Weathered Brazilian Soils

Abstract Equilibrium adsorption experiments on zinc (Zn), cadmium (Cd), copper (Cu), and lead (Pb) were conducted in three horizons of two Ultisols and one Oxisol with and without liming, from Vicosa‐MG (Brazil). Equilibrium solutions were applied as a “cocktail”; containing 700 mg L‐1 of Zn, 20 mg L#lb1 of Cd, 200 mg L‐1of Cu, and 300 mg L‐1 of Pb and its dilutions of 1:5 and 1:20. After shaking, the mixture was centrifuged, the supernatant collected and the pH and the concentrations of metals in the mixture were determined. Soil order, soil horizon, and liming had significant effects on the metal adsorption. Some important changes in the adsorption characteristics of the metals, especially in Zn and Cd, were observed due to competition between the different cations present in the solution. Also, desorption of Zn and Cd was observed with an increasing concentration of the solution. The adsorption data for Zn and Cd did not fit the linear, Langmuir, Freundlich, and Temkin isotherm equations for most situa...Abstract Equilibrium adsorption experiments on zinc (Zn), cadmium (Cd), copper (Cu), and lead (Pb) were conducted in three horizons of two Ultisols and one Oxisol with and without liming, from Viçosa‐MG (Brazil). Equilibrium solutions were applied as a “cocktail”; containing 700 mg L‐1 of Zn, 20 mg L#lb1 of Cd, 200 mg L‐1of Cu, and 300 mg L‐1 of Pb and its dilutions of 1:5 and 1:20. After shaking, the mixture was centrifuged, the supernatant collected and the pH and the concentrations of metals in the mixture were determined. Soil order, soil horizon, and liming had significant effects on the metal adsorption. Some important changes in the adsorption characteristics of the metals, especially in Zn and Cd, were observed due to competition between the different cations present in the solution. Also, desorption of Zn and Cd was observed with an increasing concentration of the solution. The adsorption data for Zn and Cd did not fit the linear, Langmuir, Freundlich, and Temkin isotherm equations for most situations, as these equations do not consider the possibility of a decrease in the amount of metal adsorbed with increasing metal competition for the adsorption sites. Due to the competition with other metals, the equations, which offered the best fit for Zn and Cd, were quadratic polynomial models. On the other hand, for Cu and Pb, the equations, which showed the best fit were linear, Langmuir, and Temkin, for different situations. The reasons for this behavior were related to the strong competitive forces for the adsorption sites presented by these two metals.

Electrochemical attributes and availability of nutrients, toxic elements, and heavy metals in tropical soils

As propriedades eletroquimicas dos solos tropicais sao muito importantes para entendimento dos fenomenos fisico-quimicos que afetam a fertilidade do solo e a disponibilidade dos nutrientes das plantas. Essa revisao destaca os atributos eletroquimicos de solos e o comportamento e a disponibilidade de nutrientes, elementos toxicos e metais pesados no solo, especialmente aqueles com predominância de minerais com cargas variaveis. A disponibilidade dos elementos e relacionada com a troca ionica, especiacao da solucao e propriedades adsortivas eletrostaticas e especificas do solo. Modelos empiricos e de complexacao de superficie sao brevemente descritos, e sao apresentados resultados de sua aplicacao em solos tropicais. E necessario um melhor entendimento do papel da dupla camada difusa de cargas e da CTC na disponibildade de nutrientes em solos altamente intemperizados, assim como uma melhor compreensao dos modelos de complexacao de superficie, a fim de melhorar o entendimento do comportamento dos ânions no solo. Mais estudos devem ser conduzidos para gerar resultados que tornem possivel o uso de conceitos de especiacao quimica e o calculo de diversas constantes usadas em modelos de complexacao, especialmente para solos altamente intemperizados do tropico umido. Deve haver um continuo desenvolvimento de programas computacionais que ja tenham incorporado os conceitos de especiacao e modelos de adsorcao no estudo da disponibilidade de nutrientes, elementos toxicos e metais pesados no sistema solo-planta.

Magnetic separation and evaluation of magnetization of Brazilian soils from different parent materials

Abstract Ten selected Brazilian soils representative of Oxisols, Ultisols, Alfisols and Inceptisols and derived from gneiss, basalt, sandstone, diabase and itabirite were sampled and examined to provide insight into the behavior of their magnetic minerals. The objective was to measure the magnetization of the sand, silt and clay fractions and to submit the clay fraction to variable magnetic fields to obtain the magnetization curves and to study their magnetic behavior as related to their parent material lithology. The separation procedure using a magnetic separator was done in two different ways: dry separation for the sand and wet separation for the silt and clay fractions. X-ray diffraction patterns of magnetic and nonmagnetic fractions were obtained and the segregation of ferrimagnetic minerals were shown. The magnetization (σs) of the total and the magnetic and nonmagnetic soil fractions was evaluated using a special analytical balance. The σs values obtained varied from 0.03 to 17.72 J T−1 kg−1 for sand; 0.05 to 8.91 J T−1 kg−1 for silt and 0.05 to 2.54 J T−1 kg−1 for the clay fractions. The results from the magnetically concentrated fractions varied in the same fashion but reached higher values. Magnetization curves showed spontaneous magnetization (Ms) values of 0.6 to 3.35 J T−1 kg−1, high field slopes (λ) ranging from 0.17 to 0.77 J T−2 kg−1 and, clearly, the influence of the parent material lithology on the nature of the soil magnetic behavior. Magnetic measurements suggested pathways for ferrimagnetic minerals transformations in soil systems.

POTASSIUM AND MAGNESIUM IN CLAY MINERALS OF SOME BRAZILIAN SOILS AS INDICATED BY A SEQUENTIAL EXTRACTION PROCEDURE

The total contents of potassium (K) and magnesium (Mg) in selected Brazilian soils (Oxisols, Ultisols, Inceptsols, and Alfisols) developed from different parent materials were investigated to estimate the contribution of clay minerals to K and Mg reserves. Total K and Mg contents in the Na-saturated clay were determined by HF total digestion. The contribution of each mineral species to the total contents of K and Mg, was estimated by a sequential mineral extraction procedure, following the order: Na-saturated clay—1) amorphous aluminum and iron oxides (ammonium oxalate); 2) crystalline iron oxides (dithionite–citrate–bicarbonate); 3) amorphous aluminosilicate and gibbsite (0.5 M NaOH); 4) kaolinite (5 M NaOH); 5) mica (NaHSO4), and 6) feldspar (HF total digestion). In order to monitor mineralogical changes, after each extraction, the samples were studied by x-ray diffraction (XRD), analytical transmission electron microscopy (ATEM), differential thermal analysis and thermo-gravimetric analysis. Total amounts of K and Mg in the clay of the strongly weathered soils were very low, indicating a low reserve of these nutrients. Due to the high proportion of kaolinite in the clay fraction of these strongly weathered soils, this mineral accounts for more than 50% of the total K and Mg. The relative proportion of kaolinite and its contribution to the K and Mg reserves increased with weathering. In strongly weathered soils, the contribution of micaceous minerals to the total K and Mg ranged from 17 to 75% and from 8 to 59%, respectively, whereas in the younger soils the range was between 51 and 83%, and 35 and 82%, respectively. Only after the removal of the iron oxides and of the kaolinite was the mica concentration in the clay fraction high enough to be detected by XRD in some of the strongly weathered soils. Dioctahedral illite was the dominant micaceous mineral due to its high resistance to weathering. Microanalysis of individual mica particles by EDAX–ATEM revealed K2O and MgO concentrations between 62 and 121 g kg−1, and between 5 and 10 g kg−1, respectively.

Extração fracionada de metais pesados em latossolo vermelho-amarelo

Samples of A and B horizons of a humic red-yellow latosol with a clayey texture were incubated in salt solutions of Cd, Cr, Cu, Ni, Pb and Zn under greenhouse conditions at the Universidade Federal de Vicosa, Brazil, from March to September 1994. The main objectives were to adapt a method for fractional extraction of metals and to evaluate their behavior in soluble, exchangeable, bound to organic matter, bound to Al oxides, bound to Fe oxides, and residual forms. The experiment consisted of two horizons and two concentrations of metal, arranged in a randomized block design with three replications. After 17 hours of incubation, the samples were air dried, homogenized, passed through a 2 mm sieve and stored in plastic bags for subsequent extraction of the metals. The samples were subjected to the methodology of fractional extraction and the evaluation of the treatment with NaOH to characterize the oxides of Al was made. The fractional extraction showed to be adequate for studying the behavior of heavy metals in soil. The Cd was found mainly in the soluble and exchangeable forms and Cr in the more stable chemical forms (bound to Fe oxides and residual); Cu and Pb presented highest affinities towards Fe oxides and organic matter, respectively. Ni was found mainly in the residual form and showed lower affinity for organic matter. The study of Zn behavior was not possible, due to the contamination of extracts stored in flasks with rubber caps. There is still a need to improve a methodology to characterize metals associated with Fe and Al oxides.

Dispersão de Latossolos em resposta à utilização de pré-tratamentos na análise textural

The accuracy of particle size analyses depends on a complete dispersion of the soil sample and the maintenance of the stability of the dispersed phase. In some Latosols the dispersion is hindered by microaggregates of high stability. These clay particles are partially detached by chemical and mechanical dispersion and because of their size, account for a systematic overestimation of the silt fraction in the analyzed soil. In order to minimize the amount of pseudo-silt in particle-size analyses of Latosols, an experiment was carried out to test how the efficacy of dispersion was affected by the use of pre-treatments for the removal of cementing agents. The treatments were set up in a factorial arrangement of 7 x 22. Study material were samples of seven Latosols dispersed with NaOH 0.01 mol L-1, with or without pre-treatment for the removal of organic matter and poorly-crystalline Fe and Al oxides. The silt fraction was dispersed again, and clay and silt proportions were determined after the second dispersion. The removal of organic matter and poorly-crystallized Fe and Al oxides increased the clay fraction yield, indicating the breaking up of microaggregates in sizes that correspond to other particle size fractions, especially silt. Pseudo-silt was found in all studied Latosols, in greater amounts in the more oxidic types. Coarse and fine sand fractions also presented clayey microaggregates that are not easily dispersed. After the second dispersion, the silt fraction presented values from 0.199 to 0.537 kg kg-1 of clay. Pre-treatments are recommended to reduce the proportion of pseudo-silt, especially the one used to remove poorly-crystalline Fe and Al oxides.

Mineralogia das frações areia, silte e argila de sedimentos do grupo barreiras no município de Aracruz, estado do Espírito Santo

To investigate the mineralogical variations with depth, 11samples were collected down to 14m, in an exposed sediment packet of the Barreiras Group in Aracruz, Espirito Santo, Brazil.The sand, silt and clay fractions were studied by X-ray diffraction, differential thermal analysis, thermogravimetry and electron microscopy.The total contents of Fe in the clay and silt fractions and Ti and Zr in the silt fraction were determined by ICP after fluoridric acid extraction.Clay and silt fractions were submitted to selective and sequential mineral extractions, to characterize and quantify their constituents.The sand fraction showed a uniform mineralogical composition, almost solely quartz, with small amounts of mica, anatase, kaolinite and iron aggregates.In the 2.1; 4.2 and 7.7m depths, the occurrence of iron mottles with dark-red colour was observed.Silt fraction, as well, is constituted mainly by quartz, with stable kaolinite aggregates and hematite.The clay fraction showed a high proportion of kaolinite, reaching 950gkg-1 at 14m depth.The low contents of Fe in the sediments and the humid conditions of the Coastal Tablelands favored kaolinite concentration and removal of minerals, mainly Fe oxides. Contents of Goethite (main Fe oxide in the sediment) decreased with depth.The amount of low cristalinity material in the clay fraction is small, varying from 3.2 to 24.0gkg-1 for ammonium oxalate extraction and from 0.6 to 3.5gkg-1 for extraction with 0.5molL-1 NaOH, due to the high degree of development of the sediments.For the same reason, the mica contents in the clay and silt fractions were lower than 5.0gkg-1.As observed for kaolinite, the mica content in the clay fraction increased with depth.