Agricultural waste as a low cost adsorbent for heavy metal removal from wastewater

Abstract

Biosorption was carried out in a batch process to test the suitability of Amaranthus hybridus (African spinach) stalk and Carica papaya (pawpaw) seed for removal of Mn (II) and Pb (II) ions from aqueous solution. The amount of metal ions removed from solution depended on the metal ion-substrate contact time, ion concentration and ion type. The contact time was 90 min for both substrates. The results indicated that the amount of absorbed metal ions varied with substrates materials, and the order of removal of heavy metals by the biosorbents was Mn (II)>Pb (II). Furthermore, Mn (II) had higher removal percentages than Pb (II) ions in both substrates. In all cases, C. papaya seeds showed greater adsorptive capacity than A. hybridus stalk. The result from both biomasses significantly fitted the Freundlich adsorption isotherm. The results obtained through the study showed both substrates are favourable for sorption and removal of heavy metal from aqueous solution. Key words: Amaranthus hybridus stalk, Carica papaya seeds, adsorption, manganese, lead, contact time.