Simultaneous adsorption–precipitation characterization as mechanisms for metals removal from aqueous solutions by cement kiln dust (CKD)

Abstract

Isotherm equations are useful for simulating adsorption data, but they cannot be easily adapted to simulate the precipitation phase. This work presents a new analytical isotherm model, based on the mass conservation principle, which can distinguish between the adsorption and precipitation mechanisms when both these processes occur simultaneously. This model was validated with the results of batch experiments conducted at the appropriate conditions using cement kiln dust as a reactive adsorbent on two metal species: copper and zinc. Thus, a new experimental procedure was established for description of the precipitation process. The developed model was found to be more representative than the conventional models in characterization of the relationship between the total sorption (adsorption–precipitation) and residual concentration of the contaminant. This model can be potentially integrated with several contaminant transport codes such as COMSOL Multiphysics 3.5a (2008), which only considers the adsorption phase. Thus, a reasonable agreement between the developed model predictions and experimental results for pure adsorption, pure precipitation, and combination of adsorption–precipitation processes was recognized.

Keywords:

• Heavy metals
• Precipitation
• Adsorption
• Contamination
• Isotherm
• Cement kiln dust