Study On Removal Of Heavy Metal Ions In Seawater By Redox

The low-temperature multi-effect distillation which has many advantages is oneof the main methods of seawater desalination and was widely used in China. Usingthe aluminum alloys is an effective way to reduce the cost of the equipment oflow-temperature multi-effect distillation. Aluminum alloys have low density, goodthermal conductivity and excellent corrosion resistance. The aluminum alloys havebeen widely used for seawater desalination technologies in present days. Thecorrosion rate of aluminum alloys in seawater can be accelerated by the heavy metalions in seawater. So it’s significant to find an effective method of removing the heavymetal ions from seawater for improving the corrosion resistance of the aluminumalloys and the stability of the desalination project.A set of equipment including the heating device, ion-exchange column and so onwhich utilized the reduction of the active metals to remove the heavy metal ions fromseawater was established in this study. The aluminum-alloy and magnesium-alloyrings filled in the ion-exchange column were used as the reducing agent and the redoxreaction of the reducing agent with Cu²⁺and Fe³⁺in seawater was utilized forremoving Cu²⁺and Fe³⁺. The effect of various factors on the removal of Cu²⁺and Fe³⁺,such as temperature, velocity of seawater, pH, salinity and initial concentration of theheavy metal ions in seawater was studied in this paper. The results indicated that Cu²⁺and Fe³⁺in seawater can be effectively removed by using aluminum-alloy ormagnesium-alloy as the reducing agent in the experiment. The efficiency of removingCu²⁺and Fe³⁺ions from seawater can be increased with the temperature and thesalinity of seawater increasing and the velocity of seawater reducing. The efficiencyof removing Cu²⁺can be increased with the initial concentration of Cu²⁺reducing, butthe efficiency of removing of Fe³⁺can be increased with the initial concentration ofFe³⁺increasing. It can also increase the efficiency of removing Cu²⁺and Fe³⁺byreducing pH of seawater when the aluminum-alloy was used. No matter the pH ofseawater increasing or reducing, it can make the efficiency of removing of Cu²⁺increased when the magnesium-alloy was used. The efficiency of removing Cu²⁺and Fe³⁺of using magnesium-alloy was higher than using aluminum-alloy under the sameoperating conditions.The surface morphologies and corrosion rate of5052aluminum alloys afterimmersed in the simulated seawater with different concentration of heavy metal ionsfor15days were also investigated in this paper. The results indicated that a largequantity of corrosion protuberances occurred on the surface of5052aluminum alloyafter adding heavy metal ions into seawater and we can also see the obviousaccumulation of corrosion products. The corrosion rate of aluminum alloy immersedin seawater containing heavy metal ions was much higher than the one immersed inseawater without heavy metal ions.According to the results, it’s a very effective method of using aluminum-alloyand magnesium-alloy as the reducing agent to remove the heavy metal ions fromseawater, such as Cu²⁺and Fe³⁺. It can efficiently reduce the concentration of theheavy metal ions in seawater which is going into the evaporator made of aluminumalloys which is used in low-temperature multi-effect distillation, so that the life of thedesalination equipment made of aluminum alloys can be extended by this method.Finally the method of using aluminum-alloy and magnesium-alloy as the reducingagent to remove the heavy metal ions from seawater can provide very effectiveprotection for using aluminum alloys in the project of low-temperature multi-effectdistillation desalination.