I want to study the effect of Al3+ ion on the adsorption behavior of a chemical reagent (e.g. fatty acid collector) on a mineral surface. The question that arises here is that what form (chemical compound) of Al3+ ion should I import in my simulation? Let's say do a speciation diagram considering all the possible species in the system, which gives me the Al(OH)3 as the stable form in the target pH range. So, does it mean I should use the hydroxide form? Its hydroxide form, however, is slightly soluble in water of the target pH range. In the literature, the chloride forms of typical metal ions have been considered, which is perfectly soluble in the water in practice. I'm looking for a logic/ criteria to make a decision on this.