Study on schwertmannite production from copper heap leach solutions and its efficiency in arsenic removal from acidic sulfate solutions

• Schwertmannite can be synthesized from copper heap leach solutions.
• Fe2 + has a significant influence on schwertmannite synthesis.
• Such Fe2 +-catalyzed transformation of schwertmannite to goethite occurs.
• Cu2 + inhibits the Fe2 +-catalyzed transformation of schwertmannite to goethite.
• As(V) in acidic solutions can be removed effectively by the synthesized schwertmannite.

Schwertmannite, a ferric oxyhydroxy sulfate mineral, has gained attention in recent years due to its high sorption capacity for toxic arsenic species. In porphyry copper mines, production of schwertmannite from heap leaching solutions may be possible because the solutions contain high concentrations of ferric and sulfate ions, which are components of schwertmannite. The present study investigates the effect of Cu2 + and Fe2 +, coexisting ions in heap leaching solutions, on the synthesis of schwertmannite; as well as the efficiency of As(V) removal from acidic solutions by the synthesized products. Synthesis was carried out by neutralization of 50 mM Fe2(SO4)3 solutions at 65 °C (final pH: 3–4), and the synthesized products were characterized by XRD. The results indicated that Cu2 + does not affect the synthesis of schwertmannite, but that Fe2 + has a significant influence on the synthesis; transformation of intermediate schwertmannite to goethite occurred in the presence of Fe2 +. Schwertmannite was produced in the presence of both Cu2 + and Fe2 +, suggesting that Cu2 + inhibits the transformation of schwertmannite to goethite in the presence of Fe2 +. To confirm this, the transformation of schwertmannite to goethite was investigated in solutions containing Fe2 + and Cu2 + at pH 3–4 and 65 °C. It was shown that a complete transformation to goethite occurred in 1 h in the presence of 100 mM Fe2 +. However, 100 mM Cu2 + inhibited the transformation of schwertmannite to goethite in the presence of Fe2 +. Batch sorption experiments were conducted to evaluate the As(V) sorption capacity of the synthesized products. The results showed that As(V) in acidic solutions (pH 3–4) can be removed effectively by synthesized schwertmannite with the maximum As(V) sorption capacity of 94–133 mg g− 1. A lower As(V) sorption capacity was observed in products containing goethite synthesized in the presence of Fe2 +; here, the maximum As(V) sorption capacity was 58 mg g− 1.