Adsorción y desorción de fósforo y elementos traza en suelos y bioadsorbentes

La presencia en el suelo de altas cantidades de elementos como el P y ciertos metales pesados/metaloides puede causar toxicidad en suelos y aguas. Es necesario el estudio de técnicas de descontaminación, entre ellas la adsorción. Se investigó la capacidad de adsorción/desorción de P y elementos traza en suelos y en varios materiales y subproductos industriales. Los resultados dependen del contaminante, del bioadsorbente y del pH. La adición de los bioadsorbentes al suelo mejora la retención edáfica. Esta investigación es útil en la gestión de áreas degradadas y en el reciclado de residuos/ subproductos

Nitrogen, phosphorus, potassium, calcium and magnesium releasefrom two compressed fertilizers: column experiments

The objective of this work was to study nutrients release from two compressed nitrogen–potassium–phosphorous (NPK) fertilizers. In the Lourizán Forest Center, tablet-type controlled-release fertilizers (CRF) were prepared by compressing various mixtures of fertilizers without covers or binders. We used soil columns (50 cm long and 7.3 cm inner diameter) that were filled with soil from the surface layer (0–20 cm) of an A horizon corresponding to a Cambic Umbrisol. Tablets of two slow-release NPK fertilizers (11–18–11 or 8–8–16) were placed into the soil (within the first 3 cm), and then water was percolated through the columns in a saturated regime for 80 days. Percolates were analyzed for N, P, K+, Ca2+ and Mg2+. These elements were also determined in soil and fertilizer tablets at the end of the trials. Nutrient concentrations were high in the first leachates and reached a steady state when 1426 mm of water had been percolated, which is equivalent to approximately 1.5 years of rainfall in this geographic area. In the whole trial, both tablets lost more than 80% of their initial N, P and K contents. However, K+, Ca2+ and Mg2+ were the most leached, whereas N and P were lost in leachates to a lesser extent. Nutrient release was slower from the tablet with a composition of 8–8–16 than from the 11–18–11 fertilizer. In view of that, the 8–8–16 tablet can be considered more adequate for crops with a nutrient demand sustained over time. At the end of the trial, the effects of these fertilizers on soil chemical parameters were still evident, with a significant increase of pH, available Ca2+, Mg2+, K+, P and effective cation exchange capacity (eCEC) in the fertilized columns, as well as a significant decrease in exchangeable Al3+, reaching values < 0.08 cmol (+) kg−1.S

Nitrogen, phosphorus, potassium, calcium and magnesium release from two compressed fertilizers: column experiments

The objective of this work was to study nutrients release from two compressed nitrogen–potassium–phosphorous (NPK) fertilizers. In the Lourizán Forest Center, tablet-type controlled-release fertilizers (CRF) were prepared by compressing various mixtures of fertilizers without covers or binders. We used soil columns (50 cm long and 7.3 cm inner diameter) that were filled with soil from the surface layer (0–20 cm) of an A horizon corresponding to a Cambic Umbrisol. Tablets of two slow-release NPK fertilizers (11–18–11 or 8–8–16) were placed into the soil (within the first 3 cm), and then water was percolated through the columns in a saturated regime for 80 days. Percolates were analyzed for N, P, K⁺, Ca²⁺ and Mg²⁺. These elements were also determined in soil and fertilizer tablets at the end of the trials. Nutrient concentrations were high in the first leachates and reached a steady state when 1426 mm of water had been percolated, which is equivalent to approximately 1.5 years of rainfall in this geographic area. In the whole trial, both tablets lost more than 80% of their initial N, P and K contents. However, K⁺, Ca²⁺ and Mg²⁺ were the most leached, whereas N and P were lost in leachates to a lesser extent. Nutrient release was slower from the tablet with a composition of 8–8–16 than from the 11–18–11 fertilizer. In view of that, the 8–8–16 tablet can be considered more adequate for crops with a nutrient demand sustained over time. At the end of the trial, the effects of these fertilizers on soil chemical parameters were still evident, with a significant increase of pH, available Ca²⁺, Mg²⁺, K⁺, P and effective cation exchange capacity (eCEC) in the fertilized columns, as well as a significant decrease in exchangeable Al³⁺, reaching values < 0.08 cmol (+) kg⁻¹

Wheat Straw as a Bio-Sorbent for Arsenate, Chromate, Fluoride, and Nickel

Batch-type experiments were used to study As(V), Cr(VI), F−, and Ni2+ sorption/desorption on wheat straw. For the lowest concentration added (0.5 mmol·L−1), the sorption sequence was F− &gt; Ni2+ &gt; Cr(VI) &gt;&gt; As(V) (93%, 61%, 29%, 0.3%), but changed to Ni2+ &gt; F− &gt; Cr(VI) &gt;&gt; As(V) when 3.0 and 6.0 mmol·L−1 were added (with 65%, 54%, 25%, 0%, and 68%, 52%, 27%, 0% sorption, respectively). Overall, As(V) showed the lowest sorption, whereas it was 25–37% for Cr(VI), 61–68% for Ni2+, and 52–93% for F−. For As(V), pH in the equilibrium solution was always above the pH of the point of zero charge (pHPZC) for wheat straw, decreasing sorption efficiency. For Cr(VI), pH was below pHPZC, but not enough to reach high sorption. For F−, pH in the equilibrium was above pHPZC, which could reduce sorption. For Ni2+, pH in the equilibrium was always below pHPZC, which made sorption difficult. The satisfactory fitting of Cr(VI), F−, and Ni2+ data to the Freundlich model suggests multilayer-type adsorption. Desorption was high for F−, whereas Ni2+ showed the lowest desorption. This research could be especially relevant when focusing on the use of wheat straw as a bio-sorbent, and in cases where straw mulching is used

Cadmium and Lead Sorption/Desorption on Non-Amended and By-Product-Amended Soil Samples and Pyritic Material

Batch-type experiments were used to study cadmium (Cd) and lead (Pb) sorption/desorption on forest soil, vineyard soil and pyritic material samples, on the by-products mussel shell, oak ash, pine bark and hemp waste, and on forest soil, vineyard soil and pyritic material amended with 48 t ha−1 of oak ash, mussel shell, and hemp waste. The main results were that the forest soil showed higher Cd and Pb retention than the vineyard soil and the pyritic material. Regarding the byproducts, sorption was in the following order: oak ash &gt; mussel shell &gt; hemp waste &gt; pine bark, with desorption following an inverse sequence. The pH was the parameter that most influenced Cd and Pb sorption. Cd and Pb sorption curves showed better fitting to the Freundlich than to the Langmuir model, indicating the dominance of multilayer interactions. Oak ash and mussel shell were the amendments causing higher increase in Cd and Pb sorption on both soils and the pyritic material (close to 100% with the oak ash amendment), as well as more a pronounced decrease in desorption. These results could be used to favor an effective management of the by-products studied, which could retain Cd and Pb in soils and degraded areas, preventing water pollution