The use of fly ash in wastewater treatment, for heavy metals (Cd, Cu and Ni,) immobilization, represents a topic much addressed to in the past years solving both, the problems of advanced treatment and the intelligent use of fly ash. The study presents the results obtained in Cd2+, Cu2+ and Ni2+ removal, using fly ash from CHP Brasov (Romania) with modified surface. Studies have compared the adsorption mechanisms of heavy metals (cadmium, copper and nickel) on fly ash with modified surface charge. The fly ash morphology is characterized using AFM while XRD provides composition and crystallinity data. Metal ions solutions (c = 10-4 – 10-2m) are mixed in a reaction flask with fly ash (powder); samples of fly ash washed in ultra pure water or with modified surfaces after long contact with alkaline (NaOH 1, 2 and 4N) solutions were used in the experiments. Using the optimized adsorption parameters (contact time, wastewater volume: adsorbent mass ratio), the adsorption isotherms are obtained and the adsorption mechanisms are discussed. The experimental data indicate that adsorption of cadmium, nickel and copper ions can be significantly improved by using the fly ash modified with NaOH 2N, when highly efficient chemical adsorption, is registered even at very low heavy metals concentrations.