Several million tons per year of water clarifier sludge are produced in Eur
ope, with forecasts of the figure doubling by the next decade. End disposal
of reference sludge is mainly based on controlled landfilling, after condi
tioning to minimise the volume of solids. The conditioning operation is car
ried-out in acidic or alkaline media, thus also allowing for coagulants rec
overy (AI, Fe species). The quality of the chemicals recovered may not be s
ufficient to justify their reuse, e.g., to water clarification operations.
With the aim of improving the purity of coagulants recovered, a new ion exc
hange process for selective removal, separation and recovery of Al(III) and
Fe(III) species from the clarifier sludge is presented. The IERAL (Ion Exc
hange Recovery of Aluminium) process is based on the use of a commercial we
ak electrolyte carboxylate resin (Purolite C106, from Purolite Co., UK), al
lowing for the removal of metals from the clarifier sludge acidic leachate
(pH 3.5), followed by selective separation and recovery of the aluminium an
d ferric species during the resin regeneration step.
Together with the performance of a fully automated 50 L/d pilot plant, this
paper reports the basic principles of the process. (C) 2000 Elsevier Scien
ce Ltd. All rights reserved.