Use of the Solubility Domain Approach for the Modeling of the Hydroxide Precipitation of Heavy Metals from Wastewater

Abstract

The use of the solubility domain approach for providing representative effluent treatment quality assurance standards for the hydroxide precipitation of Zn 2+ , Pb 2+ , and Fe 3+ from various wastewater composition types has been modeled and experimentally validated. Solubility domain calculations were based on the precipitated phases isolated from systems representing the upper and lower limits of potential effluent chemical compositions. All such phases resembled their mineralized counterparts with a lower degree of structural order. For all systems modeled, the experimentally observed solubilities were generally encompassed within the predicted solubility domains. Validation of the approach using real treatment data demonstrated the effectiveness of the solubility domain method in predicting optimum operating condition ranges for wastewater treatment. Prediction accuracy was largely dependent on the nature of the solubility-limiting phase. With the exception of carbonate-rich systems, changes to the aqueousphase complexation had a minimal impact on solubility in comparison to selection of the solubility-limiting phases.

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

“…The formation of CdSO 4 ·3.5Cd(OH) 2 ·xH 2 O and/or β-Cd(OH) 2 and CaSO 4 ·2H 2 O as separate phases suggests that no Ca 2+ -Cd(II) multi-component solid species occur during the hydroxide precipitation of Cd(II) from a SO 4 2− -rich environment in the presence of Ca 2+ . Moreover, the formation of CaSO 4 ·2H 2 O had little effect on the solubility of Cd(II), which is in agreement with previous observations in SO 4 2− -rich systems Baltpurvins et al, 1996). These studies also demonstrate the effect that Ca 2+ has on the nature of solid phases actually isolated.…”

“…Previous studies Baltpurvins et al, 1995Baltpurvins et al, , 1996Baltpurvins et al, , 1997aTünay et al, 1991) have shown that the use of chemical speciation packages for the prediction of effluent treatment performance is highly dependent on the nature of the actual solubility-limiting (i.e. solubility-determining) phases.…”

“…It is therefore critical to establish the exact nature of these solubility-limiting phases for solubility domain calculations, instead of basing these calculations simply on the thermodynamically preferred phases. Furthermore, the presence of different electrolyte types and their concentrations influence the exact nature of the solubility-limiting phases (Baltpurvins et al, 1995(Baltpurvins et al, , 1997a. In the present study, a combination of X-ray powder diffraction (XRD) and selected thermogravimetric analysis (TGA) studies were employed to characterize the exact nature of the solubility-limiting phases for each individual system.…”

“…However, little emphasis has been placed on generating guidelines for assuring an efficient hydroxide precipitation process with the variation of effluent composition. In our previous studies of other heavy metals, solubility domain predictions have been used successfully to account for the effect of anion type and concentration on the efficiency of hydroxide precipitation in the case of Zn(II), Pb(II), Cu(II) and Ni(II) using CaO or NaOH as a source of base (Baltpurvins et al, 1995(Baltpurvins et al, , 1997aLin et al, 1998). This process involves calculating precipitation profiles (i.e.…”

Effective treatment of cadmium–cyanide complex by a reagent with combined function of oxidation and coagulation

“…Thus, it is difficult to be removed by conventional hydrolysis precipitation. The addition of oxidizing chemicals is the most popular method to destroy and remove cyanides [2], and then Cd available to be removed by hydrolysis precipitation and coagulation [3,4]. Fe(VI) has been reported to be effective for treating heavy metal-cyanide complex due to cyanide oxidation by Fe(VI) and subsequent removal of heavy metal by Fe(III) coagulation [5,6].…”