Study On The Performance Of Macromolecule Heavy Metal Flocculant PEX And Its Application

In this thesis, a strong ligand of heavy metals (dithioic acid or salt group) was introducedto a macromolecular flocculant (polyethyleneimine). The new kind of flocculant synthesizedin this way has the function of trapping heavy metals and could remove not only thesubstances which cause the turbidity but also the various species of heavy metals fromwastewater. This kind of flocculant is called Macromolecular Heavy Metal Flocculant (PEX).Because PEX has the two function, it is possible to reduce some treatment units in wastewatertreatment, the wastewater treatment system could be simplified greatly.This thesis mainly researched some following contents: 1) The isoelectric point ofamphoteric macromolecule heavy metal flocculant PEX was measuered by nephelometery,and the property of PEX in the aqueous solution was also studied preliminarily. 2) Somefactors affecting the removal of heavy metals were evaluated. 3) The selective precipitation ofdifferent metal ions on PEX was studied. 4) The stabilization of PEX and the flocs wasevaluated preliminarily. 5) The application of PEX in the treatment of actual electroplatingwastewater was initially studied.The above-mentioned experimental results shows that: 1) The isoelectric point of PEX is3.00. The isoelectric point and solubility of PEX will be affected when the different salt ionsare added. At the isoelectric point, the flocculation efficiency is lower for heavy metal ionsremoval, but the flocculation efficiency is higher at the pH higher than the isoelectric point. 2)When some wastewater containing heavy metal ions is disposed by PEX, the virtue is obvious,such as the lower dosage of PEX, the shorter floe formation time, the better settleability andthe more approving water quality of the drained water. 3) The treatment efficiency of Ni²⁺,Cu²⁺, Hg²⁺, Cd²⁺, Pb²⁺ and Zn²⁺ is higher by PEX, and their concentration of the treated wateris lower than the allowable criterion. However, when wastewater containing Cr³⁺ is disposedby PEX, it is necessaryt to add inorganic aluminium salt for the higher treatment efficiency. 4)When some wastewater containing heavy metal ions is disposed by PEX, the demand for pHvalues is more flexible, that is, the treatment efficiency is higher at the acidity condition. But,pH values will affect the dosage of PEX. At lower pH values, the dosage of PEX is decreasing,in contrast, it is increasing at higher pH values. 5) When some affecting factors exist inwastewater, such as alkali metal ions, alkaline-earth metal ions, Fe³⁺, Cl^-, NO₃^-, SO₄^2-,ammonium citrate, aminoacetic acid, EDTA or humic acids, they will promote or depress theremoval of heavy metal, and these effects are not absolutely same. When they depress theremoval of heavy metal, it is effective to minish or eliminate the infection. 6) In theco-existing system for heavy metal ions and turbidity, heavy metal ions and turbidity-causingsubstance are both removed for higher removal efficiency. 7) PEX has selectivity on heavy metal ions, and a general selectivity order of Hg²⁺＞Pb²⁺＞Cd²⁺＞Zn²⁺＞Cu²⁺＞Ni²⁺ may beestablished at. 8) PEX has better stabilization at the lower temperature, and the treatmentefficiency for heavy metal will less alteration for 10 monthes. Also, the flocs has higherstabilization, so it is not easy to produce second pollution. Furthermore, heavy metal in theflocs may be regenerated. 9) When actual electroplating wastewater is disposed by PEX, thetreatment method is simple, feasible and convenience, and the treatment efficiency is higher.Therefor, PEX has good society benefit and economy benefit, and it will be applied well.In this thesis, the above-mentioned experimental results is analysed and explained intheory.