Behaviour of uranium in hydroxyapatite-bearing permeable reactive barriers: investigation using 237U as a radioindicator

Role of Phosphate in the Remediation and Reuse of Heavy Metal Polluted Wastes and Sites

“…Due to the complexity of any soil matrix, the exact immobilization mechanisms following amendments have not been clarified, which could include precipitation, chemical adsorption and ion exchange, surface precipitation, formation of stable complexes with organic ligands, and redox reaction [70]. Special attention has been devoted to immobilization of radioactive metal ions with emphasis on the long-term performance of HA as reactive material for the removal of uranium in passive groundwater remediation systems [71,72]. The formation of autunite Ca(UO 2 ) 2 (PO 4 ) 2 or chernikovite H 2 (UO 2 )2(PO 4 ) 2 was proposed as the low solubility uranium salts formed by reaction with HA [73].…”

“…Mechanisms [12,109,[125][126][127][128][129][130][131][132] Two types of apatite are particularly concerned in PRB. Calcium hydroxyapatite with the formula Ca 10 ðPO 4 Þ 6 ðOH) 2 and Ca 10Àx Na x ðPO 4 Þ 6Àx ðCO 3 Þ x ðOH) 2 so called Apatite (II), a particular form of apatite generated as a waste product from fish industry.…”

Phosphate-Mediated Remediation of Metals and Radionuclides

“…Apatite minerals have been effective in decreasing soluble concentrations (i.e., a 1,000-fold reduction) of contaminants that include Cd, Co, Cu, Hg, Mn, Ni, Pb, Sb, Th, and U [73,79,105]. Apatite reactive barriers have been effective in decreasing soluble metal and radionuclide concentrations in situ; however, the reversibility of cation adsorption and possible changes to hydraulic conductivity must be considered with this approach [34,80,81,100]. Thus, the use of apatite requires continuous monitoring of the barrier effluent under dynamic geochemical conditions (i.e., changing contaminant concentration and pH) to maintain optimal contaminant sequestration and to calculate barrier lifetime [80,100].…”

Adsorptive features of polyacrylamide–apatite composite for Pb2+, UO22+ and Th4+

“…For example, adsorptive features of Ca-hydroxyapatite in view of the influence of sorption protocol, kinetics and diffusion were investigated for Cd 2+ [9,10], UO 2 2+ [5,11], Pu 6+ [12] and Co 2+ [13] in aqueous solutions. The ionexchange features of Ba-hydroxyapatite for Cu 2+ , Pb 2+ , Zn 2+ , Cd 2+ and Co 2+ , and the enhancement of Ba 2+ exchangeability with Pb 2+ were of interest in studies performed by Sugiyama et al [14,15].…”