Purification of local chrome-containing wastewater and recovery
of chrome compounds

Summary

Domestic and international experience in wastewater recycling and reuse at various stages of leather production shows that the effectiveness of the process solutions directly depends on the chemicals used. In the practice of Russian leather factories sodium carbonate is used to precipitate chromium compounds from solutions. The results of experimental studies of the recovery of spent chrome-containing solutions from the process of skin tanning with magnesium hydroxide suspension and sodium carbonate solution are presented. The conditions of spent chrome tanning liquor precipitation using magnesium hydroxide suspension were studied. The main parameters influencing the precipitation process are pH value and precipitation agent consumption. The high efficiency of using magnesium hydroxide suspension as a precipitation agent is explained by the higher precipitation rate and absence of chromium compounds in supernatant. The main characteristics of the generated sludge are determined. Chromic hydroxide generated as a result of using magnesium hydroxide suspension is characterized by the higher density and better filterability. The possible recovery of tannic chromium compounds from precipitated chromium hydroxide is shown when dissolved in sulfuric acid and reinforced with chrome tanning agent to the required concentration. Recommendations on the use of magnesium hydroxide suspension in the process of spent chrome tanning agent recovery have been developed. The technological advantages and economic efficiency of using magnesium hydroxide as compared to sodium carbonate solution are given.

Key words

settling , chrome-containing spent solutions , filtering capacity , chrome tanning agent , chromic oxide , magnesium hydroxide suspension