Separation and Purification Technology 35 (2004) 61–70 Zinc and cadmium adsorption on low-grade phosphate Munther Issa Kandah ∗ Chemical Engineering Department, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan Received 18 November 2002; received in revised form 21 March 2003; accepted 21 March 2003 Abstract An attempt was made to utilize low-grade phosphate (LGP) as an adsorbent for Zn 2+ and Cd 2+ over a range of initial metal ions concentrations (10–50 ppm), agitation time (5–210 min), adsorbent concentration (1–7 g/l) and pH (2–6). Adsorption of both Zn 2+ and Cd 2+ increased with increased LGP concentration and reached maximum uptake at 5 g/l and pH between 4 and 6 for both metal ions. The amount adsorbed increases with time and initial metal concentrations for both metal ions. The equilibrium time was achieved for both metal ions after 30 min. The process of uptake obeys both the Langmuir and Freundlich isotherms. The affinity of LGP for H + is considerably higher than for Zn 2+ and Cd 2+ . The equilibrium uptake of zinc ions decreases with the increase in the initial cadmium ions concentration and that of cadmium ions decreases as the initial zinc ions concentration increases. Desorption of LGP with 0.1 N H 2 SO 4 was done for three cycles successfully. © 2003 Elsevier B.V. All rights reserved. Keywords: Low-grade phosphate; Zinc; Cadmium; Adsorption 1. Introduction Removal of different heavy metals from aqueous solution can be accomplished by different methods. Precipitation of the hydrous oxides is one of the most common used methods due to its simplicity and low cost [1]. However, this method produces large vol- umes of sludge that is costly and hazardous to dis- pose of and it may not reduce the heavy metal content sufficiently. Adsorption is another method that can be used for heavy metals removal in which activated car- bon is one of the most recommended adsorbents [2,3]. The high cost of activated carbon has inspired search for the development of alternatives from cheaper and ∗ Tel.: +962-79-5289570; fax: +962-2-70-95018. E-mail address: mkandah@just.edu.jo (M.I. Kandah). readily available materials. Some of the low-cost ad- sorbents already reported for the removal of heavy metals are waste tea leaves for the removal of Pb 2+ , Cd 2+ , and Zn 2+ [4], agricultural by products such as almond shells, olive stones and peach stones for the removal of Zn 2+ , Cd 2+ and Cu 2+ [5], denatured rhi- zopus arrhizus biomass for the removal of La 3+ and Zn 2+ [6], sediments of rivers for the removal of Cd 2+ , Zn 2+ , Cu 2+ , and Pb 2+ [7], rice husk [3], peanut hull [8] for the removal of Hg 2+ , bentonite [9], and zeolite [10]. In Jordan, many alternative local available low-cost adsorbents have been investigated. Gharaibeh et al. [11] proved the feasibility of using processed solid residue of olive mill products in the removal of Zn(II) and Pb(II) from aqueous solutions. Al-Degs et al. [12] investigated the technical feasibility of using diatomite 1383-5866/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1383-5866(03)00131-X