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 P-REE leaching efficiency is greater when microorganisms are in direct contact with the ore surface. This study investigated biofilm formation by the PSB Klebsiella aerogenes on the surface of monazite. Initial attachment occurred during the early hours of 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 high attachment-affinity towards the surface of P-REE, hence, playing an important role during initial attachment. Attachment occurred preferentially on larger-sized particles. Analysis of the dynamics of planktonic and sessile equilibrium during initial attachment revealed greater biofilm formation in the presence of monazite compared to a glass surface, in which lowering the initial cell concentration shifted the equilibrium towards a greater sessile population promoting biofilm formation, as did increasing the total available area. Given enough time PSBs colonise the surface of these minerals and form mature biofilms, which cover almost the whole surface. Microscopy analysis of biofilm cross-sections showed a thin-layer structure. Biofilm selectively formed on and around physical imperfections but showed no selectivity towards particular mineralogy.