The effect of copper on the precipitation of scorodite (FeAsO4·2H2O) under hydrothermal conditions: Evidence for a hydrated copper containing ferric arsenate sulfate-short lived intermediate

► Scorodite was found to form at T >138 C and >90min independent of the presence or absence of copper sulfate in the solution. ► At <96 min and 138 C an intermediate copper containing ferric arsenate sulfate phase was observed for the first time. ► Excess ferric sulfate was found to slow down the full development of H-bond structure in scorodite. ► Analysis of an industrial residue found the arsenate environment to be similar to that of intermediate basic ferric arsenate sulfate (BFAS).