A comparative study of different leaching processes for the extraction of Cu,Ni and Co from a complex matte

The extraction behaviors of Cu, Ni and Co from a complex matte under different leaching conditions have been discussed. The synthetic Cu-Ni-Co-Fe-S matte was prepared by melting the pure metals. The matte contained 24.95% Cu, 35.05% Ni, 4.05% Co, 11.45% Fe, 24.5% S, similar composition as is expected to be obtained by reduction smelting of the Pacific Ocean nodules followed by sulphidisation of the alloy. The different phases identified are CuFeS₂, CuS₂, (FeNi)₉S₈, (FeNi)S₂, Ni₉S₈, Ni₃S₂, (CoFeNi)₉S₈ and Co metal. The merits and demerits of each process of dissolution i.e., H₂SO₄/oxygen pressure leaching, atmospheric FeCl₃ leaching, NH₄OH/(NH₄)₂SO₄ pressure leaching are discussed in detail. Out of the three, the H₂SO₄/oxygen pressure leaching process is found to be the most suitable with more than 99% metal extraction efficiency within 1 h of leaching time. From the X-ray diffraction analysis, the different undissolved phases corresponding to different leaching processes have been identified. The metal extraction efficiency decreased in case of atmospheric FeCl₃ leaching and NH₄OH/(NH₄)₂SO₄ pressure leaching processes due to the formation of product layer such as elemental sulfur and goethite, respectively.