Microbially-enhanced chemisorption of Ni2+ ions into biologically-synthesised hydrogen uranyl phosphate (HUP) and selective recovery of concentrated Ni2+ using citrate or chloride ion

Hydrogen uranyl phosphate (HUP) deposited enzymatically on Citrobacter N14 immobilized in polyacrylamide gel removed nickel ions from solution via int ercalative ion-exchange into the HUP lattice. Using flow-through columns co ntaining 100 mg dry weight of biomass and similar to 200-250 mg loaded uran ium column saturation and breakthrough of Ni2+ occurred after ca. 600 ml, w ith a total of similar to 30 mg Ni2+ loaded per column, corresponding to a molar ratio of U:Ni of similar to 2:1, in accordance with the identity of t he material as Ni(UO2PO4)(2), identified previously. Ni2+ was selectively d esorbed using 100 mM sodium citrate-citric acid buffer over 140 ml or a sho rt pulse (5 ml) of 500 mM citrate buffer followed by a water wash, giving a total recovery volume of 80 ml, with a total citrate concentration of simi lar to 30 mM in the wash solution of the latter. As an alternative eluant w hich gives no residual BOD NaCl (0.6 M) or seawater gave comparable recover y of Ni2+ to the 0.5 M citrate pulse, but with a Ni2+ recovery volume of 40 -50 ml. The concentration ratio of Ni2+-deposition:desorption (vol:vol) was 3-4 fold better with chloride ion than with 100 mM citrate.