Aline Renée Coscione

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.

Direct voltammetric determination of Mo(VI) in plants: the need for a multivariate study of interferences

A multivariate modelling procedure using a second order composite design showed that the adsorptive stripping voltammetry (AdSV) technique used for molybdenum determination in a N,N-dimethylformamide (DMF)–ethanol–water homogeneous ternary solvent system (HTSS) using-benzoinoxime (BO) as the complexing agent and a sodium acetate–acetic acid buffer as the supporting electrolyte is much more tolerant to the presence of phosphorous (as phosphate) and iron than it could be presumed. Instead of the concentration ratios of P/Mo = 100 and Fe/Mo = 500, determined by univariate experiments, these values were respectively raised to 97,500 and 4200 when the phosphate and Fe(III) levels are varied simultaneously from 0.625 to 2.500 and from 0.006 to 0.150 mg l −1 , respectively, in the voltammetric cell, keeping the molybdenum concentration constant at 3.00 gl −1 . This allowed us to propose a straightforward AdSV–HTSS procedure for the determination of Mo(VI) in plants. The AdSV results compared favourably with those obtained by using graphite furnace atomic absorption spectrometry (GFAAS) and with the results of samples from the International Plant-Analytical Exchange (IPE) programme of Wageningen University (The Netherlands).

Determination of molybdenum in steel by adsorptive stripping voltammetry in a homogeneous ternary solvent system.

A new alternative approach for the determination of molybdenum in steel is proposed, using adsorptive stripping voltammetry (AdSV). The determinations are performed in a homogeneous ternary solvent system (HTSS) composed of N,N-dimethylformamide, ethanol and water, with alpha-benzoinoxime (alpha BO) as the complexing agent and a sodium acetate-acetic acid buffer as the support electrolyte. The HTSS composition was optimized by mixture design modelling. The AdSV measurements were performed in the differential pulse mode using an accumulation potential of -1050 mV. Under these optimized experimental conditions, the Mo(VI)-alpha BO reduction current peak potential is observed at potentials near -1250 mV, much lower than those usually reported, and the calibration plot follows the polynomial equation I = 0.359 + 0.265 [CMo(VI)] - 0.015 [CMo(IV)]2 (r2 = 0.997), for Mo concentrations up to 10.0 micrograms L-1. There is a linear range in this calibration plot for Mo(VI) concentrations up to 0.20 microgram L-1, defined by the equation I = 0.353 + 0.385 [CMo(VI)] (r2 = 0.980). In both cases, I is the absolute value for the current in microA and CMo(VI) is the concentration of Mo in microgram L-1. The detection limit for this linear concentration range was estimated as 20 pg L-1. A RSD of 0.43% is associated with the signals at a Mo(VI) level of 0.72 microgram L-1. From the common method-interfering species tested, only iron at Fe/Mo(VI) ratios above 500 and vanadium and tungsten at M/Mo(VI) ratios above 100 appear to affect the analytical response significantly. Phosphorous may also reduce the analytical signal at P/Mo(VI) ratios above 100, due to the formation of the competitive P-Mo complex. The suggested routine procedure was tested by analyzing four stainless steel samples and the results compared well with the ICP-AES measurements. The higher sensitivity of this method permits direct determination of Mo(VI) in steels, eliminating the need of analyte concentration or separation steps in the sample processing procedure.

Revisiting titration procedures for the determination of exchangeable acidity and exchangeable aluminum in soils

Abstract The use of 1 mol L‐1 ammonium chloride (NH4Cl) or ammonium nitrate (NH4NO3) solutions as alternative soil extractants were evaluated for the determination of the exchangeable acidity and exchangeable aluminum (Al) in twelve soil samples by the traditional titration/back‐titration method. The exchangeable Al results were compared with those obtained by inductively coupled plasma emission spectrometry (ICP‐AES) measurements while the exchangeable acidity results, using either NH4Cl or NH4NO3 solutions as alternative soil extractants, were compared against those using 1 mol L‐1 potassium chloride (KCl) and bromothymol blue as the indicator. The results indicated that the use of ammonium (NH4) salts in these determinations is not recommended since the exchangeable acidity found using these extractants was systematically higher than that found in KCl extracts due to the additional acidity caused by the presence of comparatively higher concentrations of NH4 + ions. In addition, the reaction media also ...

PLS regression using real sample calibration for aluminum and iron determination in plant extracts

Real samples were used for PLS model calibration and validation steps, showing that this approach can be of value in preventing deviations in the results caused by the matrix effects for the simultaneous spectrophotometric determination of aluminum and iron in plant extracts. One hundred UV-vis spectra, obtained from samples of the 1997 to 2000 International Plant-Analytical Exchange (IPE) program (The Netherlands), were used for model development, with ICP-AES aluminum and iron determinations as reference values for model calculation. The plant extracts were analyzed both by ICP-AES and by the PLS models developed in this work, using calibrations with both aqueous standard solutions and with real sample extracts. In addition, since the use of smaller calibration sets could be of value in reducing both the cost and the time of analysis, sets with fewer calibration samples were also investigated, with the help of the Kennard and Stone algorithm for sample selection. Comparison of the predictability of the best model obtained with each calibration set was made using the ratio of their relative root mean square error (%RMSEV) for samples in the validation set, for aluminum or iron determinations, and were compared against F-test tabulated values. For all the models developed with real samples, the differences in the %RMSEV values for the aluminum or iron determinations were found not to be statistically significant, at a confidence level of 95%. Although it was observed that the aluminum, but not the iron, determinations with the PLS 2 model prepared with aqueous standards tend to be slightly lower than the ICP-AES determinations, this model has a good global prediction ability, as observed through the correlation curves presented, and can be used for screening determinations or for other agricultural purposes.

O modelamento estatístico de misturas: experimento tutorial usando voltametria de redissolução anódica

This work illustrates the modeling procedure for a solvent mixture using the simplex- centroid approach. The selected experiment was the optimization of the peak current observed in the direct determination of nickel by anodic stripping voltammetry (ASV) in a solvent mixture composed of N,N-dimethylformamide, ethanol and water. The text is presented in a tutorial way, showing in detail the several steps which must be followed in such a process. Since not all possible mixtures lead to a measurable instrumental response, pseudocomponents had to be used to rescale the experimental design. This also allows to show how to apply this tool, usually troublesome for non-specialists in mixture modeling procedures.

Analytical methods and quality assurance

The proposed analytical protocol is applicable to potassium chloride and ammonium chloride soil extracts. It makes use of ethanol as a reaction accelerator. Full color development is achieved after a standing period of 2 hours and the absorbance measurements were performed at 555 nm, against the blank. Under these conditions the interference of other elements usually found in the soil extracts were not important. The calibration graphs, in the range from 0 to 1.0 mg L -1 Al +3 , were fitted by 2nd order polynomial regressions. The protocol was tested with 10 representative soil samples from the State of Sao Paulo (Brazil), containing exchangeable aluminum varying from 30 to 200 mg Al kg -1 of soil and variable amounts of iron. All samples were run in triplicate and the results averaged. The correlation among the proposed procedure and the measurements obtained by ICP-AES were [Al,XO] = 0.96[Al,ICP] - 7.38 with r 2 =0.9950 and [Al,XO] = 1.06[Al,ICP] - 6.43 with r 2 =0.9970, for the KCl and NH 4 Cl extractions. For absorbance readings above 0.9 or below 0.1 it is advisable to repeat the determinations by taking sample aliquots of 1.00 or 10.00 mL, respectively. This analytical approach proved to be appropriate for routine work.Abstract The proposed analytical protocol is applicable to potassium chloride and ammonium chloride soil extracts. It makes use of ethanol as a reaction accelerator. Full color development is achieved after a standing period of 2 hours and the absorbance measurements were performed at 555 run, against the blank. Under these conditions the interference of other elements usually found in the soil extracts were not important. The calibration graphs, in the range from 0 to 1.0 mg L‐1 Al+3 were fitted by 2nd order polynomial regressions. The protocol was tested with 10 representative soil samples from the State of São Paulo (Brazil), containing exchangeable aluminum varying from 30 to 200 mg Al kg‐1 of soil and variable amounts of iron. All samples were run in triplicate and the results averaged. The correlation among the proposed procedure and the measurements obtained by ICP‐AES were [Al,XO] = 0.96[Al,ICP] ‐ 7.38 with r2=0.9950 and [Al,XO] = 1.06[Al,ICP] ‐ 6.43 with r2=0.9970, for the KCl and NH4Cl extractions. For absorbance readings above 0.9 or below 0.1 it is advisable to repeat the determinations by taking sample aliquots of 1.00 or 10.00 mL, respectively. This analytical approach proved to be appropriate for routine work.

Carbon stability and mitigation of fertilizer induced N 2 O emissions in soil amended with biochar

Biochar is a promising tool for an efficient and low environmental impact agriculture since can offer both soil carbon (C) sequestration and mitigation of nitrous oxide (N2O) emissions. The extent of biochar C stability after soil amendment and efficiency in reducing N2O emissions from an external nitrogen (N) source were accessed through laboratory incubations. A clay loam soil was amended with chicken manure (CM), sewage sludge (SS), eucalyptus sawdust (ES) and filter cake (FC) feedstocks and corresponding slow-pyrolysis (400°C) biochars at 5gCkg-1 soil in combination with two N fertilizer rates (0 and 140mgNkg-1 soil). Carbon dioxide (CO2) and N2O emissions were measured during 60days. Biochars and feedstocks CO2 emissions were described by an exponential first order kinetics model. For C mineralization an interaction effect was observed for feedstock source and organic amendment. Lower values of mineralizable C was found for biochars than corresponding feedstocks, except for ES. Carbon losses in 60days of incubation totaled between 0.8 and 9.4% and 2.4 and 32% for biochars and feedstocks, respectively. Regarding to N2O emissions, only CM-biochar impacted emissions with a two-fold increase in non-fertilized soil. When NH4NO3 was co-applied, biochars reduced fertilizer induced N2O emissions, reaching a seven-fold reduction in SS-biochar treatment. The fertilizer emission factor (EF) decreased with biochar amendments as well, varying between 0.01 and 0.08% of the fertilizer N emitted as N2O, which shows the biochar potential to reduce fertilizer induced N2O emissions, with major reduction by SS-biochar mitigating 87% of the soil-fertilizer emissions. Such potential could be explored by designing biochars based on feedstock chemical and structural properties, including a mixed feedstock source biochar that promotes C sequestration and mitigates N2O emissions.

Time-based injection approach for monosegmented continuous flow systems and related techniques

A time-based injection modulefor monosegmented continuousflow systems and related techniques, which uses three independently controlled solenoid valves, is described. A timer c’cuit employing three LC. 555s and three TIP-121 transistors was constructed to control the injection module valves. The injection device was tested with non-reacting chemical systems (for example with a spectrophotometric standard and calcium flame emission) and with reacting conditions (for example the determination of Cr(VI), using diphenylcarbazide as colour reagent, and acid-base titration). The performance of this injection module demonstrates its suitabilityfor everyday use.

Estudo da especiação de arsênio inorgânico e determinação de arsênio total no monitoramento ambiental da qualidade de águas subterrâneas

This work reports an alternative, fast and robust method, for the determination of total As, As(III) and As(V) by HG-AAS without the use of prereductants. The method is based on the different rates of arsine formation of the inorganic As species and the effect of As(III) in the signal obtained for total As. Groundwater and mineral spiked waters were used to sample preservation evaluation. The method was validated by the determination of As in SRM 1640 and used in the determination of total As and its inorganic species in groundwater samples collected from mines in the Iron Quadrangle - MG.