THE RELATION BETWEEN GROUNDWATER FLOW AND HEAVY METALS CO-PRECIPITATION WITH CALCIUM CARBONATE: A REMEDIATION APPROACH

Contamination of groundwater by heavy metals is prevalent at agricultural, commercial and industrial sites across the world. In situ treatment processes can remediate subsurface contaminants of the groundwater without water extraction. This study was conducted to assess the effectiveness of carbonate precipitation for the in situ remediation of groundwater contaminated with heavy metals. Treated and standardized Quaternary sand from United Arab Emirates were placed in aquarium made of glass and was used, in this experiment, to simulate an isotropic porous media. The mean of grain size of sand used was about 0.135 mm; the study reported the mineralogy and grain morphology of the used sand. The average hydraulic conductivity of the sand was estimated to be 9.7 mm/min, while the hydraulic gradient was 0.15. The quantity of water used in this experiment was about 4.3 liter (in each run), and the time of each run was about 45 hours. Before each run, the sand was leached with distilled water. Remediation zones of carbonate solutions were designed to intercept plumes of contamination containing Pb2+, Sr2+, Cd2+, Cu2+, and Zn2+ produced by feeding of treatment solutions in the used sand. Natural attenuation of heavy metals (second run; first run was just distilled water) and attenuation as results of interception with the remediation zone (third run) were compared. The flow and gradient of groundwater, and associate heavy metal load were investigated. The study exhibited that carbonate solution can co-precipitate with the heavy metal and decrease the concentration of most metals except Sr. The results of the experiments also indicated that about 90% of Cd was precipitated within the last 10 hours of the experiment. Cadmium may have been precipitated as relatively insoluble octavite (CdCO3). The decrease of metal concentration in the second run could be due to the establishment of highly pH environment and the formation of calcite or aragonite, which provided heavy metals co- precipitation. The study concluded that the rates of remediation of heavy metals are both concentration and hydraulic properties dependent. The study also reported other data digestion activity of the reported data and limitations as well as potentials of this technique.