Preparation Of Composite Phosphating Solution And Flocculant Using Phosphate Residue

Phosphated residue was explored as raw material to make comprehensive use by two different methods:preparation of compound phosphate solution and preparation of inorganic polymer flocculant.(1) Preparation of composite phosphate solutionA kind of composite phosphating solution was prepared using solid phosphate residue. The dropping corrosion test, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) were employed to evaluate the corrosion resistance of phosphating films. The optimal phosphating films were obtained when the concentration of basic phosphating solution, zinc oxide, zinc nitrate, Manganese salt, additive, sodium molybdate were 100 mL/L,5 g/L,10 g/L,10 g/L,2 g/L,0.6 g/L respectively, the solution temperature and immersion time are 65～70℃and 750～900 s. The corrosion time of phosphating films was 72 s for CuSO4 drops. The protective effect was observed for the phosphated sample:(i) shifted towards more ennobled values of the corrosion potential by nearly 106 mV, and (ii) a significant decrease of the corrosion current density by 73.83μA-cm-2 in comparison with bare carbon steel. Phosphating films protected the carbon steel substrate well because the protection efficiency was up to 92%.(2) Preparation of inorganic polymer flocculant.According to the result of analysing the phosphated residue composition, a technical method on producing polysilicic acid-ferric and zinc sulfate (PFZSS) has been investigated. On the basis of composition of phosphated residue, temperature, acid concentration, ratio of acid to phosphated residue and stirring time were respectively examined as factors that influenced the converting efficiencies phosphated residue when soaking phosphated residue with acid solution at atmosphere. The optimal technic was that temperature, acid concentration, ratio of acid to phosphated residue and stirring time were 70℃,4 mol/L,4 ml/g,1 h, respectively. Phosphated residue dissolution rate was 96% and utilization rate sulfuric acid was 51%.The acid solution could be used as flocculant.When treating dye wastewater, the optimum pH range of coagulation was 6-8. The formed flocculant could settle in 90 min in slightly acidic medium. Removal efficiencies of COD and turbidity reached 35% and 57% respectively when the flocculant dosage of 25 mL/L was employed. Through researches done on affection to coagulation performance of PFZSS by orthogonal test, it was proved a successful condition when SiO2(%), the molar ratio of (Fe+Zn)/SiO2, the reaction time, the living time and pH of flocculant were 6%,1:2,1.5 h,2 d andl～2 respectively. PFZSS had shown a high coagulation effect, little worse to that of PAC for dye wastewater treatment at the same dosage. The optimum coagulation pH range of PFZSS is 5-7. After sedimentation period of 15min, removal efficiencies of COD and SS by this type of flocculant reached 57% and 95%, respectively. Infrared analysis showed that there were hydroxy-bridged iron to the polymer and hydroxy-bridged zinc to the polymer in PFZSS.