Sol-gel synthesis and characterization for metal ion separations from aqueous streams

Novel organo-ceramic composite materials prepared by sol-gel processing are proposed as sorbents for metal separations in wastewater treatment processes and hydrometallurgical processes. Organo-ceramic adsorbents have been developed by either solvent deposition or covalent ligand attachment techniques. These conventional organo-ceramic adsorbents have good mechanical, chemical, and thermal strengths and well defined pore characteristics. However, the applications of these conventional organo-ceramic adsorbents are limited due to low metal uptake capacity. Composite adsorbent synthesized by sol-gel processing are proposed to overcome low metal uptake capacities of the conventional adsorbents while maintaining the favorable properties of organo-ceramic adsorbents.;Three organo ceramic materials functionalized with Kelex-100, phosphonic acid, and phosphinic acid are synthesized using previous techniques and characterized for their applications. Kelex-100 based adsorbents were synthesized for separation of germanium from simulated leachate solutions. The adsorbent shows a high selectivity towards Ge(IV) and negligible adsorption of As(II), Sb(II), Ni(II) and Zn(II). Adsorption tests in a fixed bed column show a sharp breakthrough curve. Stripping of the germanium loaded column bed is achieved using 1 M HCl.;The phosphonic acid adsorbent was applied to neodymium separations. Uptake capacity increases with pH in the range from 0.5 to 6.5, and the maximum uptake capacity at pH 6 is observed to be 1.13 mmol/g. The equilibrium adsorption isotherm gives a satisfactory fit of the adsorption data. A kinetics study conducted with different concentrations and particle sizes of neodymium(III) in a batch reactor shows a high rate of adsorption of compared to literature values.;The adsorption of rare earth elements (REEs) with the synthesized phosphinic acid functionalized adsorbent was investigated in HNO3 solutions containing diethylenetriaminepentaacetic acid (DTPA), an acidic multi-dentate chelating agent. It was found that DTPA concentration and pH had significant effect on the adsorption. With increase in DTPA concentration, the adsorption of REEs onto the phosphinic acid based adsorbent decreases. Results show promise for the separation of REEs and minor actinides from high level liquid waste.;In addition to the above desirable properties, these adsorbents show high chemical stability during repeat uses, and as such, have significant potential for industrial application.