Chemical State of Aluminum in Geothermal Water

Abstract

It was found that chemical state of trace aluminum in geothermal water can be examined by the measurement of 27Al MAS NMR spectra for aluminum adsorbed and concentrated to ion exchange resins. In an acidic geothermal water of pH 2.8, aluminum was present as [Al(H2O)6]3+, on the other hand, in weak alkaline geothermal waters (pH: 8.7 and 9.2), aluminum existed as aluminosilicate complex anions with large Si/Al atomic ratio judging from the chemical shift values. In this method, however, only ionic aluminum species can be detected, but non-ionic aluminum species cannot be detected in principle. Therefore, adsorption experiment of aluminum in geothermal water to silica gel powder, which is a model compound of silica scale previously deposited, was performed at the same time. Based on results of 27Al MAS NMR measurements and adsorption experiments, the chemical state of dissolved aluminum in geothermal waters was deduced.