Preparation Of Coagulant From Fly Ash And Flocculation Produced Water Containing Polymer Combined With Electric Flocculation

Coagulating sedimentation and filtration were wildly used in treatment of oilfield produced water. With the extension and application of polymer flooding in oil field, polymer flooding wastewater is complex and difficult to deal with. The water quality problems have become increasingly prominent. The existing conventional technology to deal with oil field produced water, such as coagulation sedimentation and filtration technology, has been unable to meet the requirements of normal production of oilfield. Therefore, to develop an effective, stable and cheap treatment and recycling technology has become an urgent problem to be solved. New technology to deal with produced water including polyethylene has a significant practical value and good environmental benefits. Fly ash coagulant with electric flocculation, coupled to the pulse electric flocculation electric neutralization, electric compression strength with fly ash adsorption of inorganic polymer coagulant multicore, enmeshment advantages combined, become a pulse electric flocculated colloid stability off-vortex coagulation reaction two-way settlement separation, are one of the effective treatment methods. In this paper, the preparation of fly ash coagulant, electrolytic flocculation treatment, mechanism of chemical flocculation and electric flocculation several aspects were conducted, main research content includes the following aspects:1. Preparation of coagulant using fly ash by solid state reaction1) The reaction conditions of coagulant preparation were studied. The conditions were changed to discuss the effection of stability include the mass ratio of raw materials, calcination temperature, calcination time, solid liquid ratio and pickling time. The mass ratio of ZnO/fly ash was0.3:1, and the mass ratio NaOH/fly-ash is0.6:1, calcination2h under600℃, solid liquid ratio is0.155g/mL, pickling time for2h, the product was poly aluminum silicate zinc iron (PAFZS) flocculant.2) XRD and FT-IR characterization were applied to probe the mechanism. The results showed that, ferric metasilicate and akluminium silicate were obtained. With the calcination temperature varied from200to650℃, the reaction was more and more suficient and benefit to the aggregation. FT-IR results presented that there was a narrow peak at about1053cm-1, which was the stretching vibration of-OH, such as Al-OH-Al, Fe-OH-Fe and Zn-OH-Zn. The transmittance became lower with more ZnO added, and the stability of PAFZS was increased. The peak at above444cm-1indicated the copolymerazation of Al3+, Fe3+, Zn2+and-OH.3) The properties of PAFZS were researched based on the turbidity and polymer content. The feasible pH range was5-7. The processing effects were good no matter the polymer concentration was lower(73.14mg/L) or higher(560mg/L). When the concentration was low, the PAFZS dosage was1000mg/L, the residual turbidity was below1NTU and the residual polmer concentration was under5mg/L. While the concentration was high, the PAFZS dosage was1400mg/L, the residual turbidity was below20NTU and the residual polmer concentration was under450mg/L.4) The surface tension and ζ potential change was studied to research the Flocculation mechanism of PAFZS. The results showed the acting force was elecr-adsorption. The ζ potential decreased with PAFZS dosage increased. The surface tension firstly declined and then increased with PAFZS dosage increased. Before lowest surface tension, the mechanism was the combination of electrical neutralization and adsorption volume sweep. After lowest surface tension, the mechanism was mainly adsorption volume sweep.2. Research of produced water containing polyethylene treated by the electrolytic flocculation1) Many materials were studied for electrolytic flocculation of polymer flooding wastewater. The polar materials were stainless steel-stainless steel and soluble aluminum anode, and the iron was filled in the middle. The electrolytic flocculation parameters were oil content, the turbidity and removal rate of polymer. In electric flocculation conditions of electric flocculation time20min, plate spacing2cm, electric flocculation voltage6v, initial pH value6, the pulse frequency0.3KHz, duty ratio0.4, the removal rate of polymer reached99.9%and the turbidity fell to0.62.2) The combination of electrolytic flocculation and chemical flocculation. Many factors were considered. Under optimum conditions, the oil content was below lmg/1, the suspended solid was below5mg/l and polymer30mg/1. The results indicated the feasibility of combination.3. Mechanism research of electrolytic flocculation1) The electrochemical reaction mechanism was studied by cyclic voltammetry. The redox potential of polar materials were measured and compared. The reduction potential of stainless steel-stainless steel higher, and benefit to oxidation and demulsification. The redox peak of aluminum was lower, and good to produce Al3+. As secondary electrode material, Al3+was conductive to electro-neutralization and electro-adsorption.2) XRD(x-ray diffraction), field emission scanning electron microscopy (fsem) and infrared spectroscopy characterizations were carried out. From the results, the electrotic flocculation mechanism of polymer flooding wastewater was analyzed. The XRD indicated the product of Al(OH)3. From the FSEM results, it could be found that the product of electrolytic flocculation were of different structures. FT-IR presented the hydrogen bonding between polymer and Al(OH)3. In conclusion, the mechanism was as follows:aluminum ion generated in the anode, and hydrolyzed to Al(OH)3. The Al(OH)3adsorbed HP AM by Vander Waals force or hydrogen bonding, and then formed pellets. Finally, these pellets connected together and aggregate.4. Feasibility study of electrolytic flocculation and chemical flocculation combinationThe oilfield test was carried out through simulation test equipment to study the feasibility of electrolytic flocculation and chemical flocculation combination. Treatment process of the produced water:raw waterâ†'electrical flocculatorâ†'buffer tankâ†'dosing coagulation settlerâ†'the buffer tankâ†'modified fiber ball filterâ†'water. In produced water after treatment, oil content is less than5mg/L, the suspended solids content is less than1mg/L, polymer content is less than15mg/L levels, produced water after treatment reached A1standard of (SY5329-94).