Hazardous industrial wastewater usually contains many toxic heavy metals such as chromium, nickel, copper, zinc, lead, cadmium and mercury. The discharge of industrial wastewater containing such heavy metals without being treated not only destroys the ecological environment but also produces a negative effect when it enters animal or human bodies.
Chromium is one of the metals used in the industrial processes including stainless steel and alloy steel production, pulp production, electroplating, textile industry, metal refining, tanning, glass industry, petroleum refining, etc. Trivalent chromium existing in the waste water is generally produced from inorganic pigments, glass preparation, ceramics, etc., and it may be produced by reduction of hexavalent chromium in reducing atmosphere. Chromium ions are toxic heavy metal ions, which seriously contaminate soil and water. Therefore, it is very important to remove chromium ions in the wastewater before it is discharged into rivers or lakes.
Chromium, like other metals, can be treated in various ways such as chemical precipitation, ion exchange, membrane filtration, solvent extraction, electrochemical processes, biological methods and photo catalysis. Recently, adsorption method has been widely applied to wastewater treatment due to its simple operation and low cost.
Ri Kyong Hun, a researcher at the Faculty of Mining Engineering, has investigated the preparation of inorganic adsorbents for removing heavy metals from wastewater and other scientific and technological problems for efficient removal of chromium in wastewater by the adsorbents.
He worked on the synthesis of heavy metal adsorbents by low-temperature hydrothermal synthesis method to prepare nanocrystalline inorganic adsorbents (erdite) of 80nm in diameter and 100nm in length at 90℃ for 24h under the conditions of S/Fe > 3 and OH-/Fe > 20.
From the experiments to use the mother liquid back to the synthetic experiments, he has confirmed that a little addition of only Na2S·9H2O to the mother liquid makes it possible to effectively synthesize erdite. The removal efficiency of these sorbents for Cr(III) is above 99.8%.
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