METHOD FOR REMOVING ZINC FROM SEWAGE SLUDGE OR THE LIKE

• Main Authors: KAJIWARA YASUNOBU, KAMEYAMA HIDEAKI, MORI SUSUMU, NASU MASAFUMI, FUJITA KUNIO
• Format: Patent
• Language: English
• Published: 17.11.1998
• Edition: 6
• Subjects: CHEMISTRY; METALLURGY; TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE

PROBLEM TO BE SOLVED: To efficiently remove heavy metals, especially zinc, from sewage sludge by adding an iron salt such as ferric chloride to the sludge to regulate the pH in a specified range, then adding sodium hypochlorite to control the oxidation-reduction potential of the sludge, continuing elution for more than one day and then separating solid from liq. SOLUTION: Ferric chloride is added to the sewage sludge to control its pH to 3.5 to 4.5, then sodium hypochlorite is added to adjust the oxidation- reduction potential to 500 to 650 mV, and the mixture is agitated to start the elution of zinc. When the elution is continued for 24 hr, zinc is mostly eluted, pH of the sludge is increased, the oxidation-reduction potential is lowered, and the elution rate of zinc is decreased. Accordingly, sodium hypochlorite is again added to the sludge to be treated to increase the oxidation-reduction potential to about 650 mV, and the elution of zinc is promoted. The process is repeated for about 4 days to elute >=80% of the zinc in the sludge. Subsequently, a high molecular flocculant is added to the sludge, solid is separated from liq., and a dehydrated cake free of zinc is obtained.