Study On Banknote Printing Wastewater Treatment Using Inorgnic Polymeric Flocculants Poly-silicon Safate

This paper is composited by three parts.First,a new kind of inorganic polymeric flocculants(IPFs)--polysilicate ferro-aluminum sulfate(PSFA) was prepared ansd adopted to treat banknote printing wastewater.Experiments revealed that maximal colour removal efficiency of 98%and COD removal efficiency of 85.00%could be achieved at the optimal dosage of 30.33g/L.And the colour and COD removal results treated by the PSFA flocculant were compared with those treated by aluminum sulfate.Experimental results showed that the most attracting parts of PSFA as compared with that of Al₂(SO₄)₃ were:lower COD and colour contained effluents; less quantity and volume sludge;better dewatering behaviour and solid-liquid separation flocs;providing a possibility to eliminate the high labor intensity plate-frame pressure procedure and replace it by ordinary filtration.Therefore,the using of PSFA generally offered a lower cost of operation and maintenance choice to treat banknote printing wastewater as compared to that of Al₂(SO₄)₃.XRD results showed that PSFA exist in amorphous state and FTIR spectroscope results demonstrated that Al³⁺,Fe³⁺ and its hydrolysate in PSFA formed polyol product with poly-silicic acid.And the coagulation/flocculation mechanism of PSFA was believed to be the combation of charge neutralization,absorption and bridging,of which the latter was thought to play a major role.Second,based on the concept of "waste control by waste",a kind of polymeric silicon sulfate metal ions salt was prepared using Al³⁺ content wastewater(and Fe²⁺ content wastewater) was used to treatment wastewater.Experimental results showed that in the case of Al³⁺ content wastewater as the raw materials,the removal rate of colour and COD of wastewater were 98%and 89.88%,respectively,at the optimism dose of 140mL/L;While in the case of both Al³⁺ content wastewater and Fe²⁺ content wastewater as the raw materials,at the optimism dose of 160mL/L,the removal rate of colour and COD of wastewater were 99%and 90.70%,respectively.Experimental results also demonstrated that enhancing the wastewater's initial temperature facilitated COD removal efficiency.FTIR spectroscope was used to measure the properties of the prepared coagulant.The results of measurement showed that new kind of material had been formed.The third part of this paper is to simulate the generation of flocs with diffusion-limited aggregation(DLA) and diffusion-limited cluster-cluster aggregation (DLCA) model.Parameters such as fractal dimensions and porosity were calculated. DLA model simulation results showed that with aggregation particles rising,fractal dimensions decreased from 1.75 to 1.30 using radius of gyration method and from 1.70 to 1.40 using box-counting method,while porosity increased from 0.75 to 0.95. Simulation result also demonstrated that simulation flocs became tenuous with the increase of aggregation particles,and we have put forward a model based on the shielding effects of already aggregation particles to explain this.DLCA model simulation results showed that the fractal dimensions was about1.40.Practical experiment,with aluminum sulfate and PSFA as coagulation to treat banknote printing concentrated wastewater respectively,were also carried out to compare the fractal dimensions between actual flocs and simulation flocs.In the case of aluminum sulfate acting as coagulant,the average fractal dimensions for actual flocs ranged from 1.3647 to 1.5048 and decreased as wastewater becoming concentrated.In the case of PSFA,actual flocs fractal dimensions ranged from 1.09 to 1.40,which showed good accordance with DLCA model simulation results.Lastly,conditions as how to get compact or loose flocs was included,which contributed a lot to explore the mechanics of coagulation.