A novel electrochemical process for the recovery and recycling of ferric chloride from precipitation sludge

• Novel electrochemical process for Fe and S recovery from FeS sludge proposed.
• Fe3+ and S2− recovered at anode potential of +0.8 V vs. SHE on graphite granules.
• Up to 60% Fe recovery was achieved when feeding the process with real FeS suspension.
• Integrated FeS precipitation and electrochemical Fe3+ and S2− recovery process proven.

During wastewater treatment and drinking water production, significant amounts of ferric sludge (comprising ferric oxy-hydroxides and FePO4) are generated that require disposal. This practice has a major impact on the overall treatment cost as a result of both chemical addition and the disposal of the generated chemical sludge. Iron sulfide (FeS) precipitation via sulfide addition to ferric phosphate (FePO4) sludge has been proven as an effective process for phosphate recovery. In turn, iron and sulfide could potentially be recovered from the FeS sludge, and recycled back to the process. In this work, a novel process was investigated at lab scale for the recovery of soluble iron and sulfide from FeS sludge. Soluble iron is regenerated electrochemically at a graphite anode, while sulfide is recovered at the cathode of the same electrochemical cell. Up to 60 ± 18% soluble Fe and 46 ± 11% sulfide were recovered on graphite granules for up-stream reuse. Peak current densities of 9.5 ± 4.2 A m−2 and minimum power requirements of 2.4 ± 0.5 kWh kg Fe−1 were reached with real full strength FeS suspensions. Multiple consecutive runs of the electrochemical process were performed, leading to the successful demonstration of an integrated process, comprising FeS formation/separation and ferric/sulfide electrochemical regeneration.

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