A Study Of Calcium Sulfate Deposition On The Modified Clay Particle

Yanchang oilfield and Changqing oilfield in Ordos Basin have the present situation of multi-layer recovery,multi-water type?such as CaCl₂,Na₂SO₄ type?,high salinity and variety?4000 mg/L 94000mg/L?.Different water type of sewage water will scaling for ion reaction after mixed treatment.Produced water after treatment is mainly used as the water source of the water injection for water flooding development process.Microbial treatment oil produced wastewater has become an important development direction of this kind of wastewater treatment.During the degradation of the pollutants in mixed wastewater of different type,microbial cell surface will produce polysaccharides that is gelatinoids,gummous and with strong adhesion.When treating this scaling type water by microbial treatment process and calcium sulfate crystals will aggregate and deposit on these polysaccharides substance.It may hinder material and energy exchange of microorganism with the outside world.That will affect efficiency and effectiveness of processing.In order to illustrate the calcium sulfate deposition regularity on microbial cell surface with polysaccharide substance,the paper made the modified clay particles loaded with polysaccharide as simulation object and explore the deposition regularity of scale on the modified particle surface.In this paper,bentonite was activated by acidification and the acid bentonite is loaded with chitosan by adsorption.By XRD,FTIR,SEM and other means to identify the chitosan on the surface of clay particles as physical adsorption and the maximum adsorption capacity was 243mg/g clay.The modified clay was put into the scaling type water and the deposition process of calcium sulfate on the surface of modified clay was explored by the conductivity measurement of water.The results showed that,the 0¹4min w-as induction period of scaling and the system was in a metastable state;14min⁴5min was nucleation stage and the conductivity decreases rapidly during this period of time;45min⁶0min was the grain growth stage and the conductivity decreased slowly.While Calcium sulfate nucleation rate constant was 0.00451min^-1and the grain growth rate constant was 0.00019321min^-1.Zeta potential of calcium sulfatedeposition process of mixing the particles was between -2mV 2mV.The system had been in an unstable state with strong aggregation and precipitation.Nucleation will increase average particle diameter of the particles during deposition process.With the steady growth of the crystal,the average particle size began to increase and then decrease in the process.The induction period of scaling would be shorten and the rate of nucleation and calcium sulphate growth would be accelerated by the increases of the modified clay particles,temperature and the stirring rate.The supersaturatio of solution was effected by the concentration change of Ca²⁺ and ?SO₄?^2-.It was u-nable to form calcium sulfate crystals or crystal formation rate was slow at low ion concentration.While the rate of scale formation would increase significantly when the ion concentration was increased.