Comparative study of alternative methods for the simultaneous determination of Fe+3 and Fe+2 in leaching solutions and in acid mine drainages

In leaching solutions coming from the hydrometallurgical processing of copper sulphides, it is necessary to determine the concentrations of Fetotal, Fe+2 and Fe+3. It is known that the 5-sulfosalicylic acid (SSA) forms a red-violet complex with Fe+3 in acid media and a yellow complex with Fe+2 and Fe+3 in presence of ammonia at pH = 10. In this study, the results obtained by the SSA method are statistically compared with those obtained by 1,10-phenanthroline method, dichromate titration method and atomic absorption spectrometry. A statistical analysis demonstrated that the SSA method gives more exact and representative results than the other studied methods. The acid mine drainages and the leaching solutions, present an extremely complex matrix because to the high content of copper and arsenic, showing relationships that vary from 1:30 up to 1:1, depending on the stages of the hydrometallurgical process. Under these considerations, the SSA method allows the determination of Fe+3 directly in samples that have an iron content in the range 0.005 g L−1–18 g L−1 with a relative standard deviation (RSD) <2%.