“…On the other hand, despite the concentrations of other elements such as Mn 2+ and Cr 2+ did not exceed their corresponding threshold concentration of the formation of metal hydroxide, they are likely to be adsorbed by Cu/Fe hydroxide because the later two have high affinity toward the formers. Indeed, particularly the iron hydroxide, is the most important mineral controlling the transport of hazardous pollutant elements in the natural environment [31][32][33]. As a result, the formation of Cu/Fe hydroxide together with afterwards adsorption behaviors is thus likely accounting for the observed scaling phenomenon.…”