title: Biogenic hydroxyapatite (Apatite II™) dissolution kinetics and metal removal from acid mine drainage.
abstract: Apatite II™ is a biogenic hydroxyapatite (expressed as Ca(5)(PO(4))OH) derived from fish bone. Using grains of Apatite II™ with a fraction size between 250 and 500 μm, batch and flow-through experiments were carried out to (1) determine the solubility constant for the dissolution reaction Ca(5)(PO(4))(3)(OH) ⇔ 5Ca(2+) + 3PO(4)(3-) + OH(-), (2) obtain steady-state dissolution rates over the pH range between 2.22 and 7.14, and (3) study the Apatite II™'s mechanisms to remove Pb(2+), Zn(2+), Mn(2+), and Cu(2+) from metal polluted water as it dissolves. The logK(S) value obtained was -50.8±0.82 at 25 °C. Far-from-equilibrium fish-bone hydroxyapatite dissolution rates decrease by increasing pH. Assuming that the dissolution reaction is controlled by fast adsorption of a proton on a specific surface site that dominates through the pH range studied, probably ≡PO(-), followed by a slow hydrolysis step, the dissolution rate dependence is expressed in mol m(-2) s(-1) as where Rate(25 °C) = -8.9 × 10(-10) × [9.96 × 10(5) × a(H+)]/[1 + 9.96 × 10(5) × a(H+)] where a(H+) is the proton activity in solution. Removal of Pb(2+), Zn(2+), Mn(2+) and Cu(2+) was by formation of phosphate-metal compounds on the Apatite II™ substrate, whereas removal of Cd(2+) was by surface adsorption. Increase in pH enhanced the removal of aqueous heavy metals. Using the kinetic parameters obtained (e.g., dissolution rate and pH-rate dependence law), reactive transport simulations reproduced the experimental variation of pH and concentrations of Ca, P and toxic divalent metal in a column experiment filled with Apatite II™ that was designed to simulate the Apatite II™-metal polluted water interaction.
authors.affiliation: Department of Mining Engineering and Natural Resources, Politechnical University of Catalunya, Bases de Manresa 61-73, Manresa 08242, Catalonia, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Oliva
authors.forename: J
authors.initials: J
authors.lastname: Cama
authors.forename: J L
authors.initials: JL
authors.lastname: Cortina
authors.forename: C
authors.initials: C
authors.lastname: Ayora
authors.forename: J
authors.initials: J
authors.lastname: De Pablo
mesh_terms: D000465:Algorithms; D000818:Animals; D002118:Calcium / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry*; D005399:Fishes; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007220:Industrial Waste / Q000032:analysis*; D007474:Ion Exchange; D007700:Kinetics; D008670:Metals / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D008906:Mining; D010758:Phosphorus / Q000737:chemistry; D012995:Solubility; D014865:Waste Disposal, Fluid / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D007202:Indicators and Reagents; D007220:Industrial Waste; D008670:Metals; D010758:Phosphorus; D017886:Durapatite; D002118:Calcium