Rapid Uptake of Nickel from Aqueous Solution with a Granulometric Fraction of a Bone-Meal Char

The ability of two grain sizes of a bone-meal char (BC), BC fine and BC coarse, at immobilizing solution nickel (Ni) was investigated in batch tests, after initial reagent characterization. A sample of monetite (MA) also was tested for comparison. Starting from a Ni concentration 100 times the groundwater intervention value, the BC fine reagent (0.15-0.30 mm) was capable of rapidly depleting Ni from solution, in only 90 min, in triplicate tests at 1:200 solid/solution ratio (mass) and initial pH 7. The adjusted pseudo second-order kinetic rate for Ni uptake (0.068 g(reagent) mg(nickel)(-1) min(-1)) resulted 50 times higher than the rate reported in the literature for Ni with another bovine-bone char. Under similar conditions, Ni depletion in triplicate tests with reagent BC coarse (1.0-2.0 mm) occurred only after 2 days. With reagent MA, Ni was never totally removed. X-ray diffraction on samples of BC fine after Ni immobilization revealed the presence of a new calcium (Ca) and Ni phosphate crystalline form. Two elemental point analyses by scanning electron microscopy with energy dispersive spectroscopy indicated 6.1-13.4% (mass) Ni on grains of BC fine. Some lines of evidence helped support the uptake mechanism as replacement of framework Ca-atoms in hydroxyapatite with Ni, including the near direct proportionality between moles of Ca released to solution and moles of Ni removed. Reagent BC fine was found to be a promising component for future Ni passive removal systems.