As an approach of treatment of water treatment plant sludge, whose amount is being increased propotional to the increase of water supply, a combined method of aluminium recovery and agricultural utilization of the sludge was considered.
To recover the aluminium from the sludge with extracting agents, the sequential processes of acidification, extraction, and regeneration are tried. The optimum condition of acidification process for the maximum recovery of aluminium from sludge was ; pH=2, mixing velocity=150 rpm, operating temperature=30 ℃, and reaction time=15 min. The operation was strangly dependent on the values of pH, and it followed the pC-pH solubility.
Extraction was the process of substitution of aluminium by MDEHPA. Under the operating condition of mixing velocity=150rpm, temperature=30 ℃, reaction time=30min., extract concentration=0.1 M, and Water/Oil=2, aluminium was selectively recovered.
In the aluminium recovery process, liquid aluminium sulfide and extract were separated and recovered. 6N sulfuric acid was used as the recovering agent under the following condition ; mixing velocity=150 rpm, reaction time=10 min., Water/Oil=1/9.
Performing the pseudo LCA(Life Cycle Assessment) on resources and environment of the aluminium recovery process, 95% of aluminium recovery efficiency was estimated by mass balance approach, and 30% of sludge production was reduced. Considering the economy of the aluminium recovery process, a cost function was obtained using market price approach to calculate construction cost, annual operation and management costs, and total unit cost per ton.
