Australia is one of the main reserves of rare earth elements phosphate (P-REE) minerals. Phosphate Solubilising Bacteria (PSB) are capable of dissolving the phosphate content of such minerals. It has been demonstrated that REE leaching efficiency is greater when microorganisms are in direct contact with the ore surface. This study investigated biofilm formation by Klebsiella aerogenes on the surface of monazite.
Initial attachment occurred soon after exposure and was affected by extracellular DNA (eDNA) production, particle size, physico-chemical properties of the surface, total available area for attachment, and inoculation size. K. aerogenes produced eDNA which provides a high attachment-affinity toward the surface of P-REE, playing an important role during initial attachment. Attachment occurred preferentially on larger sized particles.
Given enough time PSBs colonise the surface of these minerals and form mature biofilms which covered almost the entire surface. Microscopy analysis of biofilm cross- sections showed a thin-layer structure. Biofilm selectively formed on and around physical imperfection but showed no selectivity toward particular mineralogy.
Cross-section analysis of the immediate surface and subsurface of the bioleached mineral samples showed extensive erosion as K. aerogenes cells broke the ore surface into small particles. Elemental depth profiling showed a significant shift in chemical composition at the microbe-mineral interface and secondary-ion mass spectrometry revealed the first empirical evidence of the formation of REE-organic acid complex formation.