Use of nanofiltration membranes to concentrate and recover leached aluminum from acidified water treatment sludge

The recovery of aluminum from water purification sludge is usually performed by making the solution acidic or basic. However, for economic reasons and reasons of safety, excessive doses of acid or base should not be utilized. Accordingly, the aluminum concentration in the leached solution is typically limited, thus the recovered aluminum cannot be directly reused as a coagulant. A nanofiltration (NF) membrane can be used in the acidic solution to concentrate high-valence metal ions. There-fore, in this work, H₂SO₄ was utilized to leach Al³⁺ ions from water purification sludge. Then, the Al³⁺ ion solution was concentrated using a low-price NF membrane. The effect of natural organic matter on the Al³⁺ ion concentrating efficiency in the filtration process has been elucidated. Experimental results reveal that Al³⁺ ions were effectively prevented from passing through the NF membrane, enabling a highly concentrated aluminum solution to be obtained. However, the presence of organic compounds may reduce the efficiency of the concentration of Al³⁺ ions in the solution.