Why apatite?

• Other phosphate phases are too soluble

  • Not persistent in the subsurface
  • Require large excesses in PO₄^-3 and metal concentrations in solution

• Process requires nucleation sites

  • Pre-existing surfaces of apatite mineral structure provide nucleating sites for precipitation of metal-phosphate phases overcoming large activation energies

• Apatites are stable in the subsurface

  • Over geological time - millions of years
  • Persistent in the face of subsurface processes
  • Does not induce microbial blooms

• Apatites are also good non-specific surface sorbers

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