Leonel Vinicius Constantino

Sorption and desorption of silver ions by bentonite clays

Anthropogenic activities have increased the concentration of metal species in the environment. The toxicity of silver ions to aquatic and terrestrial organisms has required monitoring by analytical methods, besides actions to promote its control as pollutant. Sorption and desorption processes are directly related to the mobility and availability of metal ions in the environment. In this context, clay minerals can be used for pre-concentration, removal and recovery of silver ions from aqueous solution. Herein, two bentonite clays (BaVC-1 and SWy-2) were characterised and applied to investigate the sorption and desorption of silver ions. Isotherms were fitted to the dual-mode Langmuir-Freundlich model to qualify and quantify sorption sites and evaluate the mobilisation process. The maximum sorption capacity was 743 and 849 meq kg−1 for BaVC-1 and SWy-2, respectively. Hysteresis index (HI) and mobilisation factor (MF) suggest that the desorption of silver ions in BaVC-1 is about four times more conducive compared to that in SWy-2, although both materials have demonstrated a great potential for Ag+ pre-concentration from aqueous solutions.

Sorption-desorption of antimony species onto calcined hydrotalcite: surface structure and control of competitive anions

Calcined hydrotalcite can be applied to remove anionic contaminants from aqueous systems such as antimony species due to its great anion exchange capacity and high surface area. Hence, this study evaluated antimonite and antimonate sorption-desorption processes onto calcined hydrotalcite in the presence of nitrate, sulfate and phosphate. Sorption and desorption experiments of antimonite and antimonate were carried out in batch equilibrium and the post-sorption solids were analyzed by X-ray fluorescence (EDXRF). Sorption data were better fitted by dual-mode Langmuir-Freundlich model (R2>0.99) and desorption data by Langmuir model. High maximum sorption capacities were found for the calcined hydrotalcite, ranging from 617 to 790meqkg-1. The competing anions strongly affected the antimony sorption. EDXRF analysis and mathematical modelling showed that sulfate and phosphate presented higher effect on antimonite and antimonate sorption, respectively. High values for sorption efficiency (SE=99%) and sorption capacity were attributed to the sorbent small particles and the large surface area. Positive hysteresis indexes and low mobilization factors (MF>3%) suggest very low desorption capacity to antimony species from LDH. These calcined hydrotalcite characteristics are desirable for sorption of antimony species from aqueous solutions.

Fertirrigação por gotejamento com doses de K na fase reprodutiva do tomateiro tipo italiano

Tomato is one of the most commercialized vegetables worldwide and its production is limited during some seasons of the year. Studying fertilization management of potassium (K), which is the most extracted nutrient by the tomato crop, could improve its growing conditions as well as its nutritional aspect. We evaluated the effect of K doses, applied by drip fertigation in the early reproductive stage, on productivity and content of K, Ca and Mg for Italian-type tomato under greenhouse conditions. Randomized blocks with ten replications was the experimental design the treatments consistingof five K doses (60, 120, 180, 240 and 300 mg/dm3) applied on the beginning of the reproductive phase. Until flower opening, all plots received the standard nutrient solution. The K doses up to 300 mg/dm3 did not influence the productivity of ripe and wealthy fruits, and the contents of K, Ca and Mg in the diagnostic leaves were not influenced by treatments. On some plants we observed a deficiency of Ca on the second to third bunch. Considering the results in this study, doses of K between 60 and 300 mg/dm3 applied in the phase of highest demand (fruit formation), did not influence the productivity of the Italian-type tomato.