Sulfuric Acid Digestion Research Articles

The production of high-purity gallium from waste LEDs by combining sulfuric acid digestion, cation-exchange and electrowinning

White light beads containing light emitting diodes (LED) were removed from the commercial light bulbs and treated with a complex, but easily implementable hydro-electrometallurgical method to recover pure Ga. Using concentrated H2SO4 as the digesting agent at 180 °C for 60 min resulted in > 90% efficiencies of gallium and indium solubilization by the subsequent water leaching. All metals - except for Ag – could be fixed in a strongly acidic cation-exchange resin by loading the solution into a chromatographic column. Indium, Cd, Pb and Sn are selectively eluted with 1 M HCl, while Al can be transferred into the aqueous phase using a 0.25 M NaF solution. Gallium is recovered in a pure eluate from the resin with 3 M NaOH, and finally, Y is eluted with 0.5 M Na2CO3. The cathodic deposition of Ga from the alkaline eluate was studied by potentiodynamic and galvanostatic methods. As high current efficiencies as 99% could be reached in solutions of 50 g/dm3 Ga and 6 M free NaOH at 300 A/m2 cathodic current density. Decreasing the NaOH concentration to 1.5 M resulted in a 10 ∼ 15% decrease in the current efficiency. Lower Ga concentrations also reduced the current efficiency significantly. The cell voltages were in the range of 2.1–2.4 V, yielding a relatively low (2 kWh/kg) specific energy consumption. The obtained cathodes were immersed into 2 M HCl at 55 °C, resulting in 99.999% Ga metal melted from Ti mother plates.

Assessment of Microplastics Distribution in a Biological Wastewater Treatment

Full-scale wastewater treatment facilities are not able to prevent microplastics (MPs) from discharging into natural waters and they are also associated with the land application of the sludge. This study evaluates the distribution of microfibers (MFs) in a lab-scale sequencing batch reactor (SBR) fed by synthetic wastewater (SW) for 93 days. The MFs were analyzed through optical microscopy in the mixed liquor (ML) and the effluent, and sulfuric acid digestion was applied to discriminate between natural and synthetic MFs (i.e., MPs). The results of the optical microscopy analyses were further validated through FTIR spectroscopy. A model describing the evolution over time of the MF concentration in the ML was created, accounting for the MFs entering the system through the SW and atmospheric deposition. The ratio between the MF concentration in the ML and the effluent was 1409 ± 781, demonstrating that MFs settle with the sludge. Consistently, in the ML, 64.9% of the recovered MFs were smaller than 1000 µm (average size 968 µm), while in the effluent, 76.1% of MFs were smaller than 1000 µm (average size 772 µm). Overall, 72% of MFs recovered from the ML were natural fibers and sulfuric acid digestion was successful in eliminating the natural MFs.

Does the sowing period change the grain technological quality of cowpea cultivars?

The aim of the present study was to evaluate whether the sowing period changes the grain technological quality of cowpea cultivars and to indicate which of these have the highest technological quality when grown in the Center-South region of Brazil. The experiment was conducted in a randomized block design, with a 6 x 3 factorial arrangement, using six cowpea cultivars (BRS Itaim, BRS Guariba, BRS Potengi, BRS Cauame, BRS Novaera and BRS Tumucumaque) and three sowing seasons, with four replicates. The evaluations held referred to the grain size and hydration, cooking time and crude protein content through sulfuric acid digestion. There was an interaction between cowpea cultivars and sowing dates for all analyzed variables. The sowing season alters the grain technological quality of cowpea when under the conditions of the Center-South region of Brazil, with the genotype-season effect dependent. Sowing dates in December and January generated lower technological quality of the cowpea beans. The BRS Tumucumaque cultivar possesses the best grain technological characteristics, having the largest grains with the highest crude protein content, as well as the shortest cooking time.

Optimization of increasing biochar doses with soil–plant–microbial functioning and nutrient uptake of maize

Biochar is an industrial product made from organic wastes thought pyrolysis process and its application to soil–plant systems is known to result several benefits. Care should be however needed to select the appropriate doses, as a function of soils and environmental conditions. The aim of the study was to examine the effect of increasing (0.5-, 1-, 2.5-, 5- and 10 m m%) biochar doses on some agrochemical and biological parameters of sandy soil, in an ecological farming system where there are particularly few opportunities to retain soil nutrients, enhancing biological activity. Wood-derived biochar (pyrolyzed at 600 °C) was mixed with soil. The nutrient content of the test plants was determined photometrically and by atomic adsorption after selenium–sulfuric​ acid digestion. Soil biological activity was determined by fluorescein diacetate enzyme (FDA) activity, while the microbial number was determined by the Most Probable Number (MPN) method. Our hypothesis was that appropriate biochar doses needed for improvement of general soil quality parameters, through the better soil-biological activities. Meanwhile the nutrient uptake of plants was measured and the biomass production of maize, the microbial abundance of key-important microorganisms and enzyme activities of fluorescein diacetate (FDA) was also assessed. Biochar applications were significantly increased biomass and yield of maize compare to the untreated control. Dose limit application of positive effect was also find in Arenosols . The increasing biochar doses might increase enzyme activities and can improve several microbial groups biomass which suggests a selection pressure of biochar to microbial population in soil and resulted in significantly higher root mass. Overall, the application of biochar (at a dose of 1%) was found to be effective on weakly humus (calcareous) sandy soils in terms of yield.

Extraction of Rare Earth Elements from Phospho-Gypsum: Concentrate Digestion, Leaching, and Purification

Rare earth-bearing gypsum tailings from the fertilizer industry are a potential source for an economically viable and sustainable production of rare earth elements. Large quantities are generated inter alia in Catalão, Brazil, as a by-product in a fertilizer production plant. Hitherto, the gypsum has been used as soil conditioner in agriculture or was dumped. The cooperative project, “Catalão Monazite: Economical exploitation of rare earth elements from monazite-bearing secondary raw materials,” intends to extract rare earth elements from these gypsum tailings. In this paper, a chemical process route to obtain a mixed rare earth carbonate from a monazite concentrate, was investigated. The results of the digestion, leaching, and precipitation experiments are presented and discussed herein. This includes reagent choice, process parameter optimization through experimental design, mineralogical characterization of the feed material and residues, purification of the leach solution, and precipitation of the rare earth as carbonates. The results showed that a rare earth extraction of about 90% without the mobilization of key impurities is possible during a sulfuric acid digestion with two heating stages and subsequent leaching with water. In the following purification step, the remaining impurities were precipitated with ammonium solution and the rare earth elements were successfully recovered as carbonates with a mixture of ammonium solution and ammonium bicarbonate.

Modeling and prediction of sulfuric acid digestion analyses data from PXRF spectrometry in tropical soils

ABSTRACT Sulfuric acid digestion analyses (SAD) provide useful information to environmental studies, in terms of the geochemical balance of nutrients, parent material uniformity, nutrient reserves for perennial crops, and mineralogical composition of the soil clay fraction. Yet, these analyses are costly, time consuming, and generate chemical waste. This work aimed at predicting SAD results from portable X-ray fluorescence (pXRF) spectrometry, which is proposed as a “green chemistry” alternative to the current SAD method. Soil samples developed from different parent materials were analyzed for soil texture and SAD, and scanned with pXRF. The SAD results were predicted from pXRF elemental analyses through simple linear regressions, stepwise multiple linear regressions, and random forest algorithm, with and without incorporation of soil texture data. The modeling was developed with 70 % of the data, while the remaining 30 % was used for validation through calculation of R2, adjusted R2, root mean square error, and mean error. Simple linear regression can accurately predict SAD results of Fe2O3 (R2 0.89), TiO2 (R2 0.96), and P2O5 (R2 0.89). Stepwise regressions provided accurate predictions for Al2O3 (R2 0.87) and Ki - molar weathering index (SiO2/Al2O3) (R2 0.74) by incorporating soil texture data, as well as for SiO2 (R2 0.61). Random forest also provided adequate predictions, especially for Fe2O3 (R2 0.95), and improved results of Kr - molar weathering index (SiO2/(Al2O3 + Fe2O3)) (R2 0.66), by incorporation of soil texture data. Our findings showed that the SAD results could be accurately predicted from pXRF data, decreasing costs, time and the production of laboratory waste.

PEDOGENESIS ON COASTAL TABLELANDS AREA WITH LOW RANGE ALTIMETRY IN PARAÍBA STATE

ABSTRACT Small variations of relief may change drainage and runoff and hence promote the formation of sandy surface horizons and hardened subsurface horizons (fragipans and/or duripans) in Coastal Tablelands soils. This study aimed to investigate the pedogenesis on Coastal Tablelands area with low range altimetry in Paraíba state; secondly, we also sought to contribute to the improvement of the Brazilian Soil Classification System (BSCS). Four soil profiles ware described and collected to be submitted to routine physical and chemical analysis, determination of Fe, Al and Si extracted by sulfuric acid digestion, sodium citrate-bicarbonate-dithionite and acid ammonium oxalate, sodium pyrophosphate, and mineralogical analysis in the sand and clay fractions by X-ray diffractometry. Optical density of the oxalate extract (ODOE) was also determined; the results were statistically evaluated using the R software. Microrelief variations conditioning differentiated water flows, along with the sandy texture of the surface horizons (A and E) and the lower coarse sand/fine sand ratio in the subsurface horizon, seem to promote clay accumulation in depth in the Spodosols developed on Coastal Tablelands environments. For this soils, the argilluvic (argissólico) character at the subgroup level of the BSCS should be incorporated. In addition, Al amorphous mineral phases and/or poorly crystalline play an important role in the formation of strongly cemented horizons (duripans) of the Spodosols, as also reported by other authors. Finally, the ODOE showed to be an efficient indicator of soils under podzolization process, being possible its use as a taxonomic criterion for classification of Spodosols by the BSCS.

Recovery of uranium, thorium and rare earth from industrial residues

This paper addresses the development of a process to recovery uranium, thorium and rare earth elements from an industrial residue, with a subsequent removal of U and Th from the liquor generated. Sulfuric acid digestion followed by water leaching was found to be the best method to solubilise the metals. The acid digestion was carried out with an acid sample ratio of 700 kg t−1 and a reaction time of 2 h, without temperature control. The water leaching step was performed at room temperature (25 ± 2 °C), with 1 h of mechanical stirring and 20% of solids. Under these conditions, a metal dissolution of 94%, 81% and 97% was reached for the REE, Th and U, respectively. After the metal solubilisation, a sulfuric liquor containing 0.08 g L−1 Th, 0.35 g L−1 U, 9.1 g L−1 REE, 16 g L−1 Al, 7.8 g L−1 Fe, 0.47 g L−1 Ca, 0.75 g L−1 Zn and 0.1 g L−1 Si was formed. This liquor was used in the solvent extraction stage in order to separate Th and U from the REE, as well as from other metals. The effect of the type and extractant concentration, acidity of the liquor and type and concentration of the stripping solution were investigated. The results showed that 97% of the uranium and 94% of the thorium were extracted by a mixture of 0.05 mol L−1 of Primene JM-T and 0.1 mol L−1 of Alamine 336, in a single stage. The stripping from the loaded organic phase for the simultaneous removal of U and Th can be effectively done by using 1.7 mol L−1 NaCl solution at pH 1.2.

Minerais ferruginosos e fertilidade natural de solos magnéticos do Vale do Jequitinhonha, Minas Gerais, Brasil

This study aimed at characterizing the chemical and mineralogical nature of soils derived from basic and acidic bedrocks from the Jequitinhonha Valley, Minas Gerais State, Brazil, focusing on the occurrence of magnetic minerals and its relationship with the natural fertility. The following soils were described, classified and sampled, according to the USDA Soil Taxonomy nomenclature: Typic Haplustox, Rhodic Kandiustox, Rhodic Haplustox and Typic Argiustoll. Granulometric analyzes and contents of macro and micronutrients were determined. In order to get more insights about each diagnostic soil horizon, the contents of the main metal cation oxides, specifically, iron, aluminum and manganese, were obtained by sulfuric acid digestion, and through their residual extractions with mixtures dithionite - citrate - bicarbonate and oxalate - oxalic acid. The samples were also analyzed by Mossbauer spectroscopy in an attempt to identify the main magnetic iron oxides. Maghemite (?Fe2O3) was found in all samples and magnetite (Fe3O4) was identified only for the sample Typic Argiustoll. Soils with higher magnetizations were found to have higher natural fertility.

Validation of a Sulfuric Acid Digestion Method for Inductively Coupled Plasma Mass Spectrometry Quantification of TiO2 Nanoparticles

A consistent analytical method incorporating sulfuric acid (H2SO4) digestion and ICP-MS quantification has been developed for TiO2 quantification in biotic and abiotic environmentally relevant matrices. Sample digestion in H2SO4 at 110°C provided consistent results without using hydrofluoric acid or microwave digestion. Analysis of seven replicate samples for four matrices on each of 3days produced Ti recoveries of 97% ± 2.5%, 91 % ± 4.0%, 94% ± 1.8%, and 73 % ± 2.6% (mean ± standard deviation) from water, fish tissue, periphyton, and sediment, respectively. The method demonstrated consistent performance in analysis of water collected over a 1month.

Tropical soils characterization at low cost and time using portable X-ray fluorescence spectrometer (pXRF): Effects of different sample preparation methods

ABSTRACT Portable X-ray fluorescence spectrometer (pXRF) has been recently adopted by the Soil Science community for uses in both field and laboratory, obtaining the total content of several chemical elements in a few seconds. Sulfuric acid digestion is an expensive and time-consuming laboratory analysis that provides contents of Fe2O3, Al2O3, SiO2, TiO2 and P2O5, important for soil studies. Due to few pXRF studies in tropical soils, this work aimed to compare contents of Fe2O3, Al2O3, SiO2, TiO2 and P2O5 obtained by pXRF with sulfuric acid digestion results, and to evaluate the effects of varying forms of preparing soil samples and scanning with pXRF on the resulting values in Brazilian soils. Soils were scanned in five conditions in-field (in situ) and in laboratory, evaluating varying sample preparation methods, particle sizes and soil moisture. Four pXRF scanning operational modes were tested. Linear regressions were adjusted between results of pXRF and sulfuric acid digestion. Equations were validated with an independent set of samples. Statistical analyses compared the methods of preparing the samples. Adequate linear models reached R2 of 0.99 and 0.89 for Fe2O3 and TiO2, respectively. Validation promoted R2 greater than 0.97 and RMSE and ME close to zero for both oxides. Statistical differences of pXRF results were found among the methods of preparing samples. pXRF spectrometer has great potential to obtain Fe2O3 and TiO2 content rapidly and economically with high correspondence with laboratory results of sulfuric acid digestion analysis. Varying methods of preparing the samples promote differences in the results of pXRF.

The effects of flue gas desulfurization gypsum (FGD gypsum) on P fractions in a coastal plain soil

In order to explore the possibility of using FGD gypsum in controlling P loss due to agricultural runoff, the effects of FGD gypsum on the P fraction were studied in the Yangtze River Delta coastal plains. The field experiments were conducted to identify (1) different application rates of FGD Gypsum to the P losses and (2) formation of Ca-P complexes in the soil in response to FGD gypsum applications. The field experiments consisted four rates of FGD gypsum (0, 15, 30, and 45 t/ha) in triplicate. FGD gypsum was obtained from a coal burning power plant. The “S” multi-point sampling method was used to collect samples of the uppermost soil interval in July and December of 2015. The total phosphorus (TP) in soil and plants was determined using the sulfuric acid-perchloric acid digestion method. The available phosphorus (AP) was determined using the sodium bicarbonate extraction-molybdenum-antimony anti-spectrophotometric method. The soluble reactive phosphorus (SRP) in the soil leachate was determined using the molybdenum-antimony anti-spectrophotometric method. The Visual MINTEQ 3.0 model was used to simulate the forms and distribution of the P fractions in the soil solution. The results indicated that the soil P fractions changed with application rats of FGD gypsum while the total soil P showed no significant change. The concentrations of SRP in the leachate also decreased in average of 27.5, 41.9, and 54.5%, respectively, with increasing FGD gypsum rates. The amounts of Ca2-P, Ca8-P, and Ca10-P of the calcium phosphates in the soil were significantly increased over the ranges of 44.3–68.6, 34.1–70.1, and 7.4–17.2%, while soil AP concentrations decreased. Visual MINTEQ modeling confirmed the speciation and fractionation of Ca-P compounds under the coastal plain soil conditions. The field experiments also showed that FGD gypsum applications did not affect the absorption of P by the vegetation. Experiments indicated that FGD gypsum has been shown to react with P in soil, resulting in decrease of AP and SRP and formation of insoluble Ca-P compounds and thereby decreasing the potential of P losses with surface runoff. FGD gypsum appears to be a more viable soil amendment than commercially mined gypsum to potentially achieve reductions in P losses and eutrophication of receiving waters.

OR20: Factors that Affect Survival in Type 3 Intestinal Failure; a Single Centre Experience of 978 Patients Over 37 Years

A method is developed to determine the amount of organic and inorganic phosphorus in an inorganic polymer (hydroxyapatite (HAP)) modified with an organic phosphorus-containing complexant. The simplicity and precision of the vanadate method have made it useful for measuring the total phosphorus content in phosphorus-containing organic polymers that are first digested in concentrated sulfuric acid. However, it can be important to quantify the organic and inorganic phosphorus capacities in modified (hybrid) polymers and this method does not distinguish between the two. In the current report, HAP was modified with 1-hydroxyethane-1,1-diphosphonic acid (HEDP) and a method developed to give the respective phosphorus capacities. HAP was contacted with HEDP for 17 h, 28 h, 56 h, 84 h, 112 h, and 140 h. By combining results from the sulfuric acid digestion of the modified polymer with those from a separate digestion in HCl, it was determined that there was a monotonic increase in the organic phosphorus capacity from 0.04 to 2.44 mmol/g, and a decrease in the inorganic phosphorus capacity from 4.68 to 2.54 mmol/g.

Effects of mechanical activation on lithium extraction from a lepidolite ore concentrate

Mechanical activation in order to improve lithium recovery from a lepidolite ore concentrate was investigated. The concentrate was mechanically activated using different milling times and the effect on the resulting products was evaluated by X-ray powder diffraction, FTIR spectroscopy, TG-DTG analysis, SEM and particle size analysis by laser diffraction. The mechanical activation leads to lepidolite amorphization and concomitant improvement of the reactivity by sulfuric acid digestion and water leaching. About 85% of Li recovery was achieved when the concentrate was activated for 15min and afterwards digested at 165°C, during 4h, using an acid/concentrate ratio of 650g/kg. Li recoveries above 70% were reached even using digestion temperatures lower than 100°C. However, to increase recovery, temperatures over 140°C are more suitable. Results obtained showed that is possible to apply a low temperature technology for recovering Li from hard rock minerals, using mechanical activation.

Using Thermogravimetric Analysis to Determine Carbon Fiber Weight Percentage of Fiber-Reinforced Plastics

Abstract The fiber content φ of fiber-reinforced plastics (FRPs) is a dominant influence on the mechanical performance and is therefore an essential quality measure. There is a lack of cost-efficient but precise measurement methods to determine φ of randomly distributed long-carbon-fiber-reinforced materials. Macro thermogravimetric analysis (TGA) is widely used for glass-fiber-reinforced plastics (GFRPs) as it is less labor-intense than sulfuric acid digestion. However, this method is not standardized for carbon-fiber-reinforced plastics (CFRPs). In this study, several macro TGA measurements of raw materials and FRPs were performed to measure degradation in relation to temperature, time and atmosphere. Conditions were found and validated which degraded the polymer but not the carbon fiber. Using macro TGA, it is possible to measure φ of a CFRP with an absolute error of less than 0.5 wt% compared to the actual value measured by weighing the raw materials.

Increased 3HV Concentration in the Bacterial Production of 3-Hydroxybutyrate (3HB) and 3-Hydroxyvalerate (3HV) Copolymer with Acid-Digested Rice Straw Waste

Bacterial synthesis of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) copolymer [P(3HB-co-3HV)] using the hydrolysate of rice straw waste as a carbon source was affected by the composition of the hydrolysate, which depends highly on the rice straw pretreatment condition. Acid digestion with 2 % sulfuric acid generated larger production of P(3HB-co-3HV) than 6 % sulfuric acid, but 3HV concentration in the copolymer produced with 2 % acid hydrolysate was only 8.8 % compared to 18.1 % with 6 % acid hydrolysate. To obtain a higher 3HV mole fraction for enhanced flexibility of the copolymer, an additional heating was conducted with the 2 % acid hydrolysate after removal of residual rice straw. As the additional heating time increased a higher concentration of levulinic acid was generated, and consequently, the mole fraction of 3HV in P(3HB-co-3HV) increased. Among the conditions tested (i.e., 20-, 40-, 60-min), 60-min additional heating following 2 % sulfuric acid digestion achieved the highest 3HV mole fraction of 22.9 %. However, a longer heating time decreased the P(3HB-co-3HV) productivity, probably due to the increased intermediates concentrations acting as inhibitors in the hydrolysates. Therefore, the use of additional heating needs to consider both the increase in the 3HV mole fraction and the decrease in the P(3HB-co-3HV) productivity.

Iron oxides in soils of different lithological origins in Ferriferous Quadrilateral (Minas Gerais, Brazil)

Different environmental conditions also lead to the formation of different pedogenic iron oxides, influencing soil chemistry. We examined the chemistry and mineralogical composition including various crystallographic parameters of pedogenic iron oxides of soils developed from itabirite, ferruginous dolomite, serpentinite and other parent materials. The low SiO2 contents relative to Al2O3 and Fe2O3 suggest strong desilication by the effect of the environmental conditions for all soils. The main pedogenic iron oxides were hematite and goethite, followed by maghemite. The small crystal size of goethite resulted in an increased specific surface area; also, isomorphic substitution of aluminum in goethite differed with the parent material. The highest content of soil Fe2O3 from sulfuric acid digestion found here was 701gkg−1, which was the highest value registered in the world literature with this methodology, according to the author's knowledge. The Fed content in the soils was strongly influenced by the parent material, with hematite being the more abundant iron oxide. Al-substitution indicated that hematite formation occurred in a different pedoenviroment than for goehtite. These results suggest that the effects of parent material on soil properties are important for both well weathered soils and little-leached soils, determining their drainage, P adsorption and capacity of trace element accumulation.

Spectral libraries for quantitative analyses of tropical Brazilian soils: Comparing vis–NIR and mid-IR reflectance data

Reflectance spectroscopy has great potential to monitor and evaluate soils at large scale; however, its effectiveness in predicting properties from tropical soils still needs to be tested since their mineralogy, organic matter levels, and charge and ion adsorption dynamics are different from temperate soils. Also, it is important to assess the most appropriate spectral range for quantification of specific soil property. Therefore, this study aimed to predict physical, chemical, and mineralogical soil properties using vis–NIR (350–2500nm) and mid-IR (4000–400cm−1) spectral libraries and statistically compare their modeling performances. We used 1259 soil samples distributed along four Brazilian States. Soil particle size, chemical analyses including macro and micronutrients, and oxides from sulfuric acid digestion were performed. Vis–NIR reflectance data were obtained by the FieldSpec Pro sensor while mid-IR data were collected using the Nicolet 6700 FT-IR sensor. Support Vector Machine was used as multiple regression algorithm and modeling performance was evaluated by R2, RMSE and RPIQ. This research presented a complete prediction analysis of soil properties important for survey, classification, and fertility management. Models fit very well (0.76≤R2≤0.90 and 2.81≤RPIQ≤5.62) for sand, clay, Al3+, H + Al3+, CEC, clay activity, Fe2O3, and TiO2 predictions, and showed reasonable performance (0.50≤R2≤0.73 and 1.83≤RPIQ≤3.78) for OC, Ca, Mg, SB, V%, m%, pH in H2O, oxides (Si, Al, and Mn), and Cu and Mn (micronutrients). Phosphorus, potassium and some micronutrients (Fe and B) were not reliably quantified (R2≤0.47 and RPIQ≤1.83). For both spectral ranges, performance indices were kept in testing steps, and no atypical distribution pattern was identified by residual analysis. Statistically, mid-IR spectral models showed better performance for 60% of the studied properties. For some oxides (Al, Fe, Ti, and Mn), vis–NIR models were better. Models developed from vis–NIR and mid-IR spectral libraries are effective and useful to quantify properties suggesting soil mineralogy, reactivity, fertility and acidity of tropical Brazilian soils; however, mid-IR is the greatest potential spectral range. The excellent results of clay (0.85≤R2≤0.88 and 3.88≤RPIQ≤5.56) and sand (0.85≤R2≤0.90 and 4.85≤RPIQ≤5.62) modeling prove that at least soil particle size analyses can be efficiently replaced by the reflectance spectroscopy methods.

Determination of Trace Germanium in Plant Samples by Dry Ashing-Atomic Fluorescence Spectrometry

To reduce the limit of detection (LOD) and allow the accurate determination of Ge, a dry ashing method was performed to enrich the Ge in plant samples. A method for the determination.of trace Ge in plant samples by HG-AFS was established. Study of the effect of temperature on the ashing of plant samples showed that no volatile loss of Ge occurred even at 900 °C. Additional experiments indicated that a 4 h burning process at 600 °C would be sufficient to fully ash the plant samples. Various digestion methods (involving nitric acid, hydrofluoric acid, and sulfuric acid digestion methods) for ashed samples were investigated. High-temperature ashing with large sample weights was used, which could reduce the reagent doses and the method's LOD effectively and simultaneously, the precision of the method was improved. The method's LOD was 0.27 ng · g(-1), and the relative standard deviation was 3.99%-6.81%. Verified with national biological reference materials (grade I), the proposed method was accurate and reliable.

Potentially toxic elements (PTEs) in soils from the surroundings of the Trans-Amazonian Highway, Brazil.

The Trans-Amazonian Highway (TAH) is located in the northern region of Brazil, comprising a border region where agricultural, mining, and logging activities are the main activities responsible for fostering economic development, in addition to large hydroelectric plants. Such activities lead to environmental contamination by potentially toxic elements (PTEs). Environmental monitoring is only possible through the determination of element contents under natural conditions. Many extraction methods have been proposed to determine PTEs' bioavailability in the soil; however, there is no consensus about which extractor is most suitable. In this study, we determined the contents of PTEs in soils in the surroundings of TAH after mineral extraction with diethylenetriaminepentaacetic acid-triethanolamine (DTPA-TEA), Mehlich I, and Mehlich III solutions. Soil samples were collected in areas of natural vegetation in the vicinity of TAH in the state of Pará, Brazil. Chemical attributes and particle size were determined, besides concentrations of Fe, Al, Mn, and Ti by sulfuric acid digestion, Si after alkaline solution attack, and poorly crystalline Fe, Al, and "free" Fe oxides. Mehlich III solution extracted greater contents from Fe, Al, and Pb as compared to Mehlich I and DTPA-TEA and similar contents from Cd, Mn, Zn, and Cu. Significant correlations were found between concentrations of PTEs and the contents of Fe and Mn oxides as well as organic carbon and soil cation exchange capacity. Contents of Cu, Mn, Fe, and Zn by the three methods were positively correlated.