Leaching of Polar Herbicides in the Presence of Designed Carbon Sorbents in Soil

Imidazolinones are polar herbicides with high leaching potential making them potential threat to environment quality. Biochar, a carbon sorbent, can efficiently stabilize substances and could be used to reduce the pesticides leaching. This work was conducted to study biochar effects on leaching of imazapic, imazapyr, and a mixture of them (Onduty®) for the first time. Leaching columns were used during lab experiments. Soil amendment with biochars produced from oil palm empty fruit bunch and rice husk significantly reduced the herbicides leaching percentages. 16% of imazapic was leached from biochar-free soil. For rice husk and empty fruit bunch biochar-amended soils the amounts were 4.3% and 3.6%, respectively. The highest percentage of imazapyr was leached out from non-amended soil (14.2%) followed by rice husk (4.0%) and empty fruit bunch (2.8%) biochar-amended soils. 15.2% of the applied Onduty® was leached from non-amended soil. Rice husk and empty fruit bunch biochars could reduce the herbicide leaching to 4.2% and 3.0%, respectively. Soil amended with biochars retained the higher percentages of the herbicides in top 7.5 cm depths. Total herbicides amounts adsorbed by biochars were more than 95%. It was concluded that biochar application has the potential to decrease imidazolinones leaching and their environmental pollution.

Solubility and Efficiency of Rock Phosphate Fertilizers Partially Acidulated with Zeolite and Pillared Clay as Additives

Soluble phosphates are the most common sources currently used in crop production in tropical soils; however, they present low efficiency and are more expensive than natural rock phosphates. The objective was to develop new phosphate fertilizers with slow solubility through the partial acidification of rock phosphates (RPs), incorporating materials with adsorption characteristics to favor slow dissolution and prevent phosphorus (P) fixation in the soil. Three rock phosphates, Araxá (ARP), Bayovar (BRP) and Morocco (MRP), were evaluated at two acidulation levels (25 and 50% Ac.) and two additives; pillared clays (PILC) and zeolites (Zeo), plus triple superphosphate (TSP) and a control (nil-P). The soil diffusion was evaluated in concentric rings in Petri dishes. Solubility was evaluated in leaching columns and sampled in layers from surface for P forms in the soil profile. The relative agronomic efficiency (RAE) was evaluated in maize. Greater diffusion was provided by TSP, followed by BRP and MRP both with 50% Ac. + Zeo, and MRP with 50% Ac. + PILC. Percolated P was more pronounced under TSP, followed by RPs (BRP and MRP) with 50% Ac. + Zeo. BRP and MRP + 50% Ac. were the most promising sources with RAE above 74% compared to TSP.

Miscible displacement of copper in soil columns using increasing doses of bentonite

The objective of this research was to evaluate the effect of applying increasing doses of bentonite to the soil on the miscible displacement of copper, quantifying copper retention in the soil and elimination by leachate, in order to prevent potential risks for environmental contamination. The experiment was conducted on a laboratory using leaching columns filled by a sandy texture soil contaminated with 250 mg kg-1 of copper each. The experimental design was a completely randomized with four doses of bentonite, 0; 30; 60 and 90 t ha-1, and three replications totalizing 12 experimental units. The leaching columns were made with PVC tubes constituted by three rings, overlaid and joined with silicone glue. Each column was filled with 4 kg of Cu contaminated soil, mixed with the doses of bentonite specified by the treatments (0; 45; 90 and 135 g). After the filling of the columns, each one received five pore volumes of distillated water, and left to percolation under a steady state flux. After percolation, the Cu concentrations in the soil and in the percolate, the breakthrough curves of the flux density and the percolation velocity were determined. The results were submitted to variance analyses using the F test and regressions. The increasing doses of bentonite until 90 t ha-1 increased the adsorption of copper by the soil, reducing the percolation of this element around 72%. Bentonite application to the soil decreased the flux density and flux velocity of the copper percolation, diminishing the potential risks for the environment contamination.

Removal of Copper Ions from Aqueous Solution by Bentonite Clay Applied in Soil in Leaching Columns

The objective of this research was to evaluate the effect of bentonite applied in soil, on the removal of copper (Cu) from aqueous solutions, in leaching columns. The experiment was carried out at laboratory using leaching columns filled with 4 kg of soil mixed with bentonite according to treatments B0, B30, B60 and B90, that is, 0; 30; 60 and 90 t ha-1 of bentonite. Each leaching column (experimental unit) was constituted of a PVC tube, with 0.10m of diameter and 0.50m height sectioned in two 0.20 m rings (10-30 cm and 30-40 cm) and one, on the top, of 0.10 m high, reserved for a hydraulic head of 0.08 m. The columns were placed in a vertical support and saturated with distilled water by capillary ascension. Then percolation began, passing through the column five volumes of pores (initially four liters of water contaminated with 1000 mg of Cu and afterwards one liter of distilled water). Ten leached aliquots of 0.5 volume of pores were collected and stored in polypropylene flasks in a refrigerator for quantification of copper (Cu) by atomic absorption spectrophotometry. At the end of the tests, the solid material contained in each ring was collected and the Cu concentration determinated. Increasing doses of bentonite increased Cu retention in soil; Cu was more retained in the surface layer in all treatments; there was no copper leaching from the columns with 60 and 90 t ha-1 of bentonite application, indicating that all copper was retained in the soil avoiding thus potential risks for groundwater contamination.

Evaluating dispersive potential to identify the threshold electrolyte concentration in non-dispersive soils

Use of non-traditional and marginal quality saline sodic water will increase in water limited environments and methods to assess use suitability are required. The threshold electrolyte concentration (CTH) defines the soil solution concentration, for a given soil solution sodicity, at which an acceptable reduction in the soil hydraulic conductivity (10–25%) is maintained without further soil structural degradation. The traditional method of determining CTH is via leaching columns, which are laborious and often expensive. Dispersive potential (PDIS) is potentially a more rapid method with which to determine the CTH in a practical sense and make management recommendations for water quality use on a given soil. This work evaluated the PDIS method against known CTH data to determine the efficacy of use for non-dispersive soils irrigated with marginal quality saline sodic water. Results suggest that the PDIS approach to CTH did not reliably, or efficiently, determine the CTH in non-dispersive soils equilibrated with an irrigation solution. Using it to determine the aggregation and dispersion boundary for initially non-dispersive soil appeared to have merit, but only where the aggregates equilibrated with the irrigation solution were subject to rapid dilution with deionised water.

Water magnetization and phosphorus transport parameters in the soil

ABSTRACT There are scientific studies describing changes in properties of the water when subjected to the action of a magnetic field, which may favor the availability of some nutrients in the soil solution. Some nutrients, although they are essential to the process of crop development, can be sources of pollution for watercourses and soil. The aim of this study was to evaluate the effect of water magnetization on transport parameters of the phosphate ion in a Red Latosol (RL) and in a Quartzarenic Neosol (QN). Saturated leaching columns were connected to bottles containing KH2PO4 solutions. In RL, there were significant differences in phosphorus (P) transport parameters, related to the retardation factor (R) and distribution coefficient (Kd). For the others, Peclet number (Pe), dispersive-diffusion coefficient (D) and dispersivity (λ), there were no significant differences in the comparison between the treatments with magnetized and non-magnetized water. In QN, there were statistical differences in R and Kd. For the other parameters, Pe, D and λ, there were no statistical differences between treatments.

Use of steel slag to neutralize acid mine drainage (AMD) in sulfidic material from a uranium mine

Acid Mine Drainage (AMD) is one of the main environmental impacts caused by mining. Thus, innovative mitigation strategies should be exploited, to neutralize acidity and prevent mobilization of trace elements in AMD. The use of industrial byproducts has been considered an economically and environmentally effective alternative to remediate acid mine drainage. Therefore, the objective of this study was to evaluate the use of steel slag to mitigate acid mine drainage in a sulfidic material from a uranium mine, as an alternative to the use of limestone. Thus, increasing doses of two neutralizing agents were applied to a sulfidic material from the uranium mine Osamu Utsumi in Caldas, Minas Gerais State. A steel slag from the company ArcelorMittal Tubarão and a commercial limestone were used as neutralizing agents. The experiment was conducted in leaching columns, arranged in a completely randomized, [(2 x 3) + 1] factorial design, consisting of two neutralizing agents, three doses and one control, in three replications, totaling 21 experimental units. Electrical conductivity (EC), pH and the concentrations of Al, As, Ca, Cd, Cu, Fe, Mn, Ni, S, Se, and Zn were evaluated in the leached solutions. The trace element concentration was evaluated by ICP-OES. Furthermore, the CO2 emission was measured at the top of the leaching columns by capturing in NaOH solution and titration with HCl, in the presence of BaCl2. An increase in the pH of the leachate was observed for both neutralizing agents, with slightly higher values for steel slag. The EC was lower at the higher lime dose at an early stage of the experiment, and CO2 emission was greater with the use of limestone compared to steel slag. A decrease in trace element mobilization in the presence of both neutralizing agents was also observed. Therefore, the results showed that the use of steel slag is a suitable alternative to mitigate AMD, with the advantage of reducing CO2 emissions to the atmosphere compared to limestone.