Extraction of heavy metals from simulant citrate leachate of sewage sludge by ion exchange

A shortage of natural resources has led to a focus towards the use of sewage sludge as a fertiliser source due to its high phosphate content. One of the main issues with the use of sewage sludge as a fertiliser source is the concentration of heavy metals, particularly copper, lead and zinc. Economical alternatives to regular lixiviants (sulphuric acid, nitric acid, etc.) for the leaching of heavy metals from solids are weak complexing acids. Ion exchange technology offers an effective method for the recovery of these metals from the leachate. This study presents the pH dependence of Cu, Fe, Pb and Zn recovery from citrate media by the ion exchange resins TP214, MTS9100, MTS9570, MTS9301, MTS9501 and C107E. Copper recovery was found to be maximised by the use of either TP214 at a pH of 5 or MTS9301 at a pH of 2. The phosphonic acid functionality containing resins, MTS9570 and MTS9501 were found to be the most effective for the removal of iron at a pH of 2 and 5, respectively. TP214 and MTS9570 show promising results for the recovery of lead, with the caveat of large copper and iron recovery, respectively and MTS9301shows high affinity towards zinc at high pH, although poor separation from copper