Proposal of a controlled release of citrate by solubility equilibrium.

Some substances at high concentrations in both the body and the environment can be toxic. The remediation of contaminated environments, for example by metals in toxic concentrations is a fairly current problem. In this way, organic acids of low molecular weight, because they are biodegradable, constitute an alternative potentially for their use in phytoremediation processes. Among these acids, citric acid was chosen to be used in this work due to its suitable binder behaviour, with high stability constants. The purpose of this work was to develop a controlled release of citrate that allows its release to the soil solution to pre-defined concentrations by the system and that this concentration is maintained even if the binder is consumed in the complexation of metals, diluted or percolated. In this way, the system has an additional feature, compared to the conventional controlled release system. The presence of calcium citrate allowed for a slower release of citrate compared to citrate soluble salts or even with calcium citrate directly in solution. The Noyes-Whitney model allowed to explain the effects of pellet sizes and percentages of agar-agar. The pH of the receptor solution and the calcium concentrations used in the preparation of the gels influenced the equilibrium concentration of the citrate, demonstrating the independence of the controlled release process in relation to other variables in the solution. The controlled release system proposed in this work is a promising and very useful system for phytoextraction processes.

Characterization and evaluation of sorption potential of the iron mine waste after Samarco dam disaster in Doce River basin - Brazil.

The Fundão dam collapsed releasing 60 million tons of mining waste into the environment. The mining wastes should be better studied, since some of them are deposited on the alluvial plains soil and at the bottom of the rivers, like sediments, of the region affected. Thus, this work aims to perform the chemical, physical and adsorptive characterization of the samples colleted in region de Paracatu de Baixo. The mining waste has uneven surface, with sizes ranging from 2 to 200 µm, pHPCZ in 6.0. Are composed predominantly by kaolinite, goethite, hematite, gibbsite and quartz. It has been classified as non-hazardous residues. The adsorption studies showed the mining waste have a low Cationic Exchange Capacity. The sorption process was occurs by ion exchange and the kinetics follows the pseudo second order model (R2 > 0.78). The process is endothermic (ΔH in 29.33 kJ mol-1) and spontaneous (ΔG in -24.7 kJ mol-1 at 25 °C). The Langmuir model presented a better fit (R2 > 0.995) to the experimental data. Therefore, the methylene blue can be used as a cation model to predict the behavior of cationic species on the mining waste, with maximum adsorption capacity of 4.42 mg g-1 at 25 °C.