(119d) Competitive Adsorption of Nickel, Manganese, Chromium and Cadmium From Aqueous Solutions by Different Adsorbents

Landfilling is the primary solid waste disposal method in Jordan. Since Jordan is considered one of the poorest countries with water resources, it is crucial to protect its groundwater resources from any possible risk of contamination from landfill leachates. A survey on leachates from landfills of different ages and control systems in Jordan, performed by our group during the years 2009 and 2010, showed that heavy metals concentrations in leachates were high exceeding the allowable limits of both Jordan Industrial wastewater and US Environmental Protection Agency. The main heavy metals with high risk are identified to be: Cr (0.66-20.5 mg/L), Mn (0.41-10.37 mg/L), Cd (0.48-4.5 mg/L), and Ni (0.74-6.69 mg/L). In the present study, competitive adsorption of these four metals on different adsorbents including: natural untreated shrimp shells (SH), granular activated carbon (GC), acid-treated granular activated carbon (AGC) and acid-treated powder activated carbon (APC) were investigated under simulated conditions.  All adsorption isotherms were generated using the bottle point method, following the ASTM standard procedure (ASTM D3860-89a). Untreated granular carbon (GC) was the best adsorbent for Ni removal from a simulated solution with 90% removal efficiency. AGC and APC both showed very high selectivity for Cr over other present metals with removal efficiency of 99%. For Mn, shrimp shells (SH) was the best adsorbent with 79% removal efficiency, while both GC and SH adsorbents have comparable efficiency for Cd removal from the simulated solution (92%). Order of metals selectivity for SH adsorbent was Cd > Mn > Ni > Cr, for GC the selectivity was Cd > Ni > Cr > Mn, for both AGC and APC the order was Cr > Cd > Ni > Mn.