The environment and its compartments have been severely polluted by unscientific dumping of hazardous wastes such as obsolete electronic goods, electroplating waste, painting waste, and used batteries along with Municipal Solid Waste (MSW) in many countries. These hazardous wastes are not segregated from MSW before being dumped in open dumpsites. Thus, causing great damage to surface water and groundwater. The open dumpsites cause environmental degradation because of open burning, surface and groundwater pollution, and soil pollution. Heavy metals released from hazardous wastes inevitably enter via leachate and it requires a paramount attention due to their toxic nature and implications on plant, animal, and human health. A combination process of adsorption followed by reactive precipitation is proposed for the separation of heavy metals before its discharge into receiving water bodies. Adsorption is one of the most effective treatment options for the separation of toxic metal ions in aqueous solutions. In this research work, activated carbon and fuel ash were used for the adsorption experiments. Composite adsorbents were prepared by two different methods: (i) using white cement as binding agent (PAC-PFA-WC), and (ii) by polymer application technique (PAC-PFA-PVA). A composite bifunctional resin was also synthesized by a polymerization technique for chromatographic fractionation of lithium from aqueous solution. The adsorbents were characterized using FTIR, XRD, SEM, and porosimetry analysis. The adsorption behavior, kinetics and thermodynamics were studied. It was found that the adsorption followed pseudo-second order reaction rate kinetics. However, it was established that intraparticle diffusion or liquid diffusion was not the sole rate limiting step. The adsorptive reactions were found to be spontaneous as well as feasible based on the estimation of thermodynamic parameters. The results demonstrate that the proposed method proves to have a synergistic behavior in the separation of toxic heavy metals from dumpsite leachate. A possible reactive mechanism for the separation of cationic metal species in the presence of other organic constituents in the actual leachate was also proposed. The adsorption capacities of toxic heavy metals using composite adsorbents were 1.24 – 3.60 and 1.07 – 7.43 fold more than activated carbon and fuel ash, respectively. Subsequently, continuous-leachate-flow studies were conducted using actual dumpsite leachate to evaluate the performance of the combination process in the separation of heavy metals. It was found that 74% - 96% and 93% - 100% separation of heavy metals was possible using PAC-PFA-WC and PAC-PFA-PVA, respectively, at a leachate flow rate of 3 L/hr with the residual concentrations of heavy metals (except lead) well within the prescribed discharge limits. An effective immobilization technique was also implemented and evaluated using diffusivity coefficient and leachability index for the environmentally-safe disposal of used adsorbents. Cement-based solidification using 1:3 mixing ratio was effective in immobilization of heavy metals. The solidification study was also supported by USEPA recommended ANSI/ANS 16.1 leaching test.