Geochemical behaviour of heavy metals in sludge effluents and solid deposits on the Zambian Copperbelt: Implication for effluent treatment and sludge reuse

Abstract Sludge effluents and solid deposits generated from the conventional lime treatment processes on Zambian Copperbelt have led to reports of copper (Cu) cobalt (Co) contamination into nearby water bodies. To better understand behaviour metals; partitioning, adsorption their specific binding forms were studied through sequential extraction, batch experiments surface complexation modeling (SCM). Results mineral composition analyses indicated that micas, kaolinite, quartz feldspar are abundant with hydrous ferric oxide (HFO) precipitates formed as a result weathering biotite grains existing grain coating. Sequential extractionrevealed Cu Co metals partitioned in order of: exchangeable (F1: 600–1500 mg/kg Cu; 100–200 mg/kg Co), acid-soluble (F2: 2200–5500 mg/kg 190–220 mg/kg Co) reducible fraction (F3: 260–300 mg/kg Co). Metals F1 hosted by F2 both kaolinite HFO whereas F3 dominantly HFO. Equal concentration between is due limited amount (i.e. 5–10 g/kg) desorption loosely adsorbed surfaces. Batch revealed dominant metal retention mechanism. According predictions, sites sites. At site; >(s)FeOCo+, showed decrease 40% single system 25% binary pH 7 - 7.5 competition for The high 0.5–1.1% Cu) displaced low 0.03–0.07% present sludge, thus rendering mobile environment. keep stable release, optimal suggested during lime. this pH, decreased below regulation standard values less generation voluminous sludge. Adsorbed can be recoverable sludge acid at