Fig. 6shows the profile of digested copper as a function of pH. In general the digested copper profile is somewhat scattered, but generally, the concentration of digested copper decreases with an increase in the pH. The issue with scattered data could be linked to analytical issues arising due to the complex organic matrixof the pot ale wastewater and the strong colour of the sample which would have had a detrimental effect on the photometer reading. At the
original pH a considerable difference in the raw and filtered sample readings can be observed. From filtering alone, a reduction of almost 50% of copper is achieved which suggests that a high proportion of copper in the pot ale wastewater is insoluble and bound to solids. This is agreement with other studies reported in the literature. Graham et al. [1] found total concentration of copper in pot ale to be in the range 2–5 mg/L, of which on average less than 50% was in solubleform.Quinn et al. [24] found total copper concentration in pot ale in the range 2.1–2.3 mg/L, of which a fraction varying in the range 20–70% was in soluble form. By increasing the pH to 8 orabove, onlya
very low copper concentration was left in the filtrate, so indicating that, by a process of solid–liquid separation coupled with pH adjustment, more than 80% of the copper in pot ale can be precipitated out of the solution. Our results are consistent with the hypothesisthat copper is removedvia precipitation as hydroxide. The reaction of copper hydroxide precipitation at alkaline pH can be described by the reaction below