A novel clinoatacamite route to effectively separate Cu for recycling Ca/Zn/Mn from hazardous smelting waterwork sludge

Cu/Zn/Mn-rich sludge was massively produced in the smelting industries, and legally recycled to reduce its product and to regenerate chemical products. In the past decades, the Cu was commonly recycled as halite from metallic leachate by the classical extraction method, but herein, was effectively purified as copper chloride hydroxide via an advanced hydrothermal route. The results showed that the sludge was carbonate substance comprised of 4.3% Cu, 1.1% Ca, 6.6% Zn and 28.7% Mn, and then completely dissolved as metallic solution by chloride acid. The adsorption of Cu onto the precipitates was investigated via the elution experiment. The results showed that when the solution was directly adjusted to pH 3.5 or 4, the coprecipitation occurred, led to the removal of 90.3–99.5% Cu, 15.5–21.6% Ca, 14.8–18.9% Zn and 11.1–19.1% Mn. But when the solution was hydrothermally treated with the addition of urea, 95% Cu was removed as clinoatacamite, but the loss of Ca/Zn/Mn were only 0.27%, 2.17% and 0.96%, separately. The adsorption of Cu onto clinoatacamite was only 0.02 g/g. In the hydrothermal reaction, the urea was spontaneously decomposed as ammonia and CO 2, to consume the newly H + that generated from the Cu hydrolysis, resulting in continuing the Cu removal at high level. The optimized parameters for Cu removal were at 140 °C for 10 h with the addition of 0.2 g urea. After the Cu removal, Ca/Zn/Mn were rest at high concentration in the treated solution, and stepwise separated as gypsum, gunningite and hausmannite, via the conventional precipitation and extraction routes. The hydrothermal recycling of Cu from metallic solution avoided the conventional multistep of extraction, stripping and evaporation, and showed potential application in the resource utilization of hazardous waste.