Qusey Muhsin Muhammad Jewad Khaliefa

The pollution of groundwater by organic or inorganic pollutants, originating from either soil leaching or anthropogenic activities, is one of the major environmental issues. Remediation of this water source is of highest priority because many countries use it for drinking purpose. Pump-and-treat method is represented for many decades the major technique to treat groundwater infected with organic/inorganic pollutants. In last two decades, this technique becomes to be in lack with the sense of modern concepts of sustainability and renewable energy. Permeable reactive barriers (PRBs) technology was introduced as an alternative method for traditional pump-and-treat systems to remediate contaminated groundwater that was achieving these concepts. Within this issue, this technology has been proven to be a successful and most efficient promising method used by many researchers and in several projects due to its direct and simple techniques to remediate groundwater. A rapid progress from bench scale to field scale implementation in the PRB technique is recognized through the last few years. In addition, this technique was modeled theoretically for characterizing the migration of contaminants spatially and temporally through the barrier and, consequently, these models can be used for estimating the longevity of this barrier. An overview of this technique and the promising horizons for scientific research that integrates this method with sustainability and green technology practices are presented in the present study.

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.

Copper and zinc ions were removed from synthetic acidic aqueous solutions onto cement kiln dust (CKD) particles in a single component system. The objectives of this study were to: distinguish between adsorption and precipitation when both mechanisms are occurring simultaneously; define their individual contributions; and consequently, specify the dominant mechanism. This was achieved by conducting a new experimental procedure for the precipitation phase that depended on CKD leachate in combination with a derivation of a simultaneous adsorption- precipitation equation. High removal efficiencies, approaching 100 %, of the Cu and Zn ions, were attained. Precipitation was the dominant mechanism for removing low concentrations of these metals, while adsorption appears to be more significant in removal of high metal concentrations.

Copper and zinc ions were removed by total sorption, adsorption and precipitation, from synthetic aqueous solutions onto CKD particles, a waste by-product, in single component system. The unique aspects of the present study were; distinguishing between the adsorption and precipitation mechanisms when both these processes occur simultaneously, finding the individual contributions of each one and, consequently, specifying the predominant mechanism. These aspects were achieved by conducting a new experimental procedure for precipitation phase depended on CKD leachate in combination with a derivation of simultaneous adsorption-precipitation equation. The results showed that high removal efficiencies, approaching 100%, of copper and zinc ions were attained and the precipitation mechanism was the predominant for removing the low concentrations of these metals, inversely; the adsorption mechanism was the predominant in the removal of high metal concentrations.

The hydraulic conductivity and breakthrough curves of copper and zinc contaminants were measuredin a set of continuous column experiments for 99 days using cement kiln dust (CKD)-filter sand as thepermeable reactive barrier. The results of these experiments proved that the weight ratios of the cementkiln dust-filter sand (10:90 and 20:80) are adequate in preventing the loss of reactivity and hydraulicconductivity and, in turn, avoiding reduction in the groundwater flow. These results reveal a decreasein the hydraulic conductivity, which can be attributed to an accumulation of most of the quantity ofthe contaminant masses in the first sections of the column bed. Breakthrough curves for the descriptionof the temporal contaminant transport within the barrier were found to be more representative by theBelter–Cussler–Hu and Yan models based on the coefficient of determination and Nash–Sutcliffe effi-ciency. The longevity of the barrier was simulated for the field scale, based on the laboratory columntests and the values verified that cement kiln dust can be effectively used in the future, as the reactivematerial in permeable reactive barrier technology. These results signify that the longevity of the barrieris directly proportional to its thickness and inversely to the percentage of the CKD used.