Silicate minerals are ubiquitous constituents of terrestrial environments and through chemical weathering provide a continual supply of dissolved silica (silicic acid). Silicic acid like many other oxyanions has a high affinity for iron oxides surfaces and binds covalently forming inner-sphere surface complexs. However, unlike other oxyanions, silicic acid has been shown to polymerize on iron oxide surfaces at concentrations far below solution saturation. The conditions under which polymerization occurs (pH, Si solution concentration, and surface coverage) are poorly understood. In the present study we investigate the adsorption kinetics and polymerization of silicic acid on goethite as a function of pH, Si concentration, and percent surface coverage using ATR-FTIR to. Additionally, the effect of monomeric and polymeric Si surface species on ligand promoted dissolution is evaluated to examine the role of Si in iron bioavailabilty.