INVESTIGATION OF THE SURFACE-PROPERTIES OF SOLID-PHASE HYDROUS ALUMINUM-OXIDE SPECIES IN SIMULATED WASTE-WATER USING ATOMIC-FORCE MICROSCOPY

Hydrous aluminum oxide particles precipitated from simulated wastewate r were examined using atomic force microscopy in order to understand t heir structural and coating properties. Three types of particles were examined: aluminum oxides coprecipitated by adding alum in the presenc e of a solution of phosphates and tannic acid; postprecipitated partic les formed by adding phosphates and tannic acid to already formed alum inum oxides; and a control case consisting of particles precipitated i n the absence of either phosphate or organic component. Using tapping mode and phase imaging atomic force microscopy, it was found that the postprecipitated particles had distinctly different viscoelastic prope rties than either of the other two particle types and also varied mark edly in particle size and morphology. These observations are consisten t with a model in which the postprecipitated particles are coated with an organic coating of tannic acid. The results are discussed in the c ontext of the relative effectiveness of these aluminum oxides in remov ing phosphates and other contaminants from wastewater during sewage tr eatment.