Design of surface functionalization of waste material originated charcoals by an optimized chemical carbonization for the purpose of heavy metal removal from industrial waste waters

► Waste material (Lapsi seeds) was chemically modified to obtain a low-cost adsorbent. ► Surface functionalization was designed to optimize the number of functional groups. ► The adsorption of heavy metals (Pb, Ni) was highly effective in aqueous solution. ► A new mechanism was proposed for functionalization and for metal ion binding. ► The adsorption's mechanism was complex formation, desorption's one was ion-exchange.