Abstract
Industrial production operations generate huge amounts of heavy metals enriched sludge. Due to inadequate management and illegal disposal practices, this waste sludge can deteriorate human and environmental health. For sustainable environmental development and conserving human health, sludge should be recycled to recover the heavy metals and the treated sludge (with permissible or safe limits of heavy metals) should be used to improve the soil fertility and physical properties. Herein, a study is carried out to identify the optimum concentration of sulphuric acid (H
2
SO
4
) to remove copper (Cu), nickel (Ni) and chromium (Cr) from the waste sludge and the number of organic matter residues that remained after the acid digestion. Besides, the optimum pH to precipitate Cu, Ni, and dissolute the Cr in the form of metal hydroxide is determined. Acid digestion is done by using H
2
SO
4
and precipitation is done by sodium hydroxide (NaOH). The heavy metals concentrations were determined through inductively coupled plasma-optical emission spectroscopy (ICP-OES). The result showed that the concentration of H
2
SO
4
is significantly affecting the sludge organic content. The respective percentage of Cu, Ni and Cr removed by 30% of H
2
SO
4
were 98.99, 99.27 and 97.22%. At pH 14, Cu, Ni and Cr precipitation to form metal hydroxide was the highest. About 4.01%, 23.75% and 13.93% of copper hydroxide, nickel hydroxide and chromium hydroxide are, respectively, precipitated out. However, slight dissolution occurred due to the nature solubility of metal hydroxide.