Copper (Cu) and lead (Pb) treatment via two-stage pH-controlled fluidized-bed non-seeded granulation process

The two-stage pH-controlled fluidized-bed non-seeded granulation process for treating Cu and Pb was explored. This investigation specifically examined operational conditions including Cu-to-Pb molar ratio (MR₁), metal-to-carbonate molar ratio (MR₂), hydraulic retention time (HRT), and first-stage pH (pH₁). Multilayered, spherical, brittle, light blue granules were recovered. X-ray diffraction only detected cerussite (PbCO₃) crystals, while the Pb Pourbaix diagram and solubility curve confirmed the cerussite stability. Meanwhile, the presence of bicarbonate could feasibly alter the prevailing voltage potential, generating the Cu-hydroxide interface in water. Furthermore, copper species in granules possibly formed amorphous solids due to low copper levels and inhibition of ionic Pb. Besides PbCO₃ crystals, the development of amorphous Cu-carbonate hydroxide could also occur during granulation. The transition to pH 8.0 in the second stage could affect the solid solubility and the surface charge influencing the accumulation and the agglomeration, respectively. Operational conditions also significantly impacted particle growth, total removal, and accumulation rates. The sub-optimal condition was found at MR₁ = 5.0, MR₂ = 1.5, HRT = 22.5 min, and pH₁ = 7.5 producing relatively high percentages of large granules, high removal efficiencies > 99 %, and accumulation rates between 80 % and 95 %.