Heavy Metals in Wastewater: The Effect of Electrolyte Composition on the Precipitation of Cadmium(II) Using Lime and Magnesia

Abstract

The effect of effluent composition on the efficiency of hydroxide precipitation of Cd(II), using both lime and magnesia as precipitants, has been modelled by the solubility domain approach in order to provide wastewater effluent treatment limits, and has been experimentally validated. Common anionic species such as Cl − , SO 4 2− and CO 3 2− have been treated. Solubility domain calculations were based on those phases that were found to determine metal solubility for systems representing the upper and lower limits of potential effluent chemical compositions. The isolated phases were found to resemble their mineralized counterparts, although in several cases exhibited a lower degree of structural order. Experimentally determined Cd(II) solubilities were generally encompassed within the calculated solubility domains, indicating that solubility domain predictions provide effluent treatment quality assurance ranges for the hydroxide precipitation process. The formation of gypsum (CaSO 4 ·2H 2 O) and calcite (CaCO 3 ) at higher SO 4 2− and CO 3 2− concentrations as secondary precipitates using lime as the precipitant, and the hydroxy-sulfate Mg 2 (OH) 2 SO 4 ·xH 2 O, nesquehonite (MgCO 3 ·4H 2 O), hydromagnesite [Mg 5 (OH) 2 (CO 3 ) 4 ·4H 2 O] and brucite [Mg(OH) 2 ] when employing magnesia was shown to have little effect on the observed residual Cd(II) solubility, although Mg(OH) 2 did promote β-Cd(OH) 2 formation in the Mg 2+ -containing Cd(II)/Cl − and Cd(II)/SO 4 2− systems.

A comprehensive review on Cd(II) removal from aqueous solution

“…From Table 1, it is seen that a removal efficiency of 100% has been achieved using the process adopted by Lin et al [16]. Furthermore, almost all the papers on hydroxide precipitation studied in this review have been able to reach a residual Cd(II) concentration of 1.0 mg/L or below, which satisfies the guidelines of US EPA and IS 10500 for discharging the effluent into a surface water body.…”

“…As an example of the effective nature of hydroxide precipitation, removal efficiencies exceeded 98% for Cd 2+ , using spiked well waters and river waters [13][14][15]. Lin et al [16] used both lime and magnesia as precipitant to treat wastewater and analysed the effect of effluent composition on the efficiency of hydroxide precipitation for Cd(II) removal. Magnesia (Mg (OH) 2 ) has been found to be a more efficient precipitant than lime due to its capability to form highly insoluble b-Cd(OH) 2 .…”

Review of Eco-Friendly Biochar Used in the Removal of Trace Metals on Aqueous Phases

“…It has proven to be carcinogenic and persistently cumulative poison [107]. Cadmium exposure to humans at long terms causes renal dysfunction whilst elevated concentrations of exposure cause bone defects, cadmium pneumonitis, increased blood pressure, obstructive lung disease, osteomalacia, osteoporosis and spontaneous fractures and myocardic dysfunctions [103].…”

Heavy Metal Pollutants in Wastewater Effluents: Sources, Effects and Remediation

“…It is indicated to be carcinogenic and persistently cumulative poison (Lin et al, 2005). A long term exposure to cadmium in humans may lead to renal dysfunction; while high exposure levels could cause obstructive lung disease, cadmium pneumonitis, bone defects, osteomalacia, osteoporosis and spontaneous fractures, increased blood pressure and myocardic dysfunctions (Duruibe et al, 2007) On the other hand, mercury is known as one of the most dangerous metals for human consumption, for it has no known biochemical function.…”