Upflow and dowflow clay biomass columns fot the removal of U (VI)

M. OLIVELLI; G. CURUTCHET; R. M. TORRES SÁNCHEZ

Rio de Janeiro

Conferencia; XV International Clay Conference; 2013

In previous studies was demonstrated that biopolymers generated from fungal biomass and a montmorillonite (BMMTs) were efficient as biosorbentes in batch uranium removal systems. BMMTs showed high adsorption efficiency even at low concentrations. Also, using very low concentrations BMMT reached their saturation only after several cycles during U(VI) progressive adsorption experiments. The objective of this work is to evaluate their metal exchange capacity by potentiometric titration and evaluate the U(VI) sorption capacity of BMMT systems for its removal from effluents. Downflow and upflow BMMT columns were performed in order to compare and optimize the system for continuous sorption techniques. Also, elution of downflow columns with diluted H2SO4 was performed. Both columns were fixedbed columns with a volume of 0,8 ml. In the continuous removal experiences, both type of columns were loaded with a solution of 25 ppm U(VI). For upflow columns a peristaltic pump was used at a flow rate of 0.65 ml/min. The total proton consumption of the studied materials indicated that there were more available sites to exchange protons in BMMTs than in MMT. Downflow columns presented a non constant flow, resulting in an inefficient method for these sorbents. The saturation of the column was reached with a very low volume, making the calculation of a breakthrough point not possible to. A possible explanation for this behaviour could be that during the load of the column a hydration process of the material could take place generating an increase in the adsorption specific surface of the biopolymer components. Data from U(VI) extraction after saturation of downflow BMMT columns indicated the possibility of recycling the BMMT after processes of U(VI) sorption, because U(VI) elution from the column was complete. For upflow columns, the U(VI) removal percentage was around of 83.3% from 150 ml of loading, 75% from 150 to 300 ml and near 58% from 300 to 400 ml. The total amount of U(VI) retained during the first 500 bed volumes, was near 20 mg U(VI) / g BMMT; leading to a yield ten times higher than that of downflow columns. Also, neither the montmorillonite nor the fungal biomass alone allowed the development of a column experiment due to the mechanical instability of the material when the solution passed trough the column. On the other hand, BMMTs presented a suitable stability of the biomaterial for the development of adsorption columns. These results indicated that upflow columns presented an advantageous performance for being applied in a greater scale and that they could be used in the development of economic and efficient biofilters