At present, most of China's oil fields have entered the secondary and tertiary oil recovery periods, mostly using water injection development methods, which result in high water content in the production fluid, and some even reach 90% [1] . If the produced water is directly discharged without treatment, it will cause serious environmental pollution and is also a great waste of water resources. Therefore, it is an urgent problem to solve the problem that the oilfield sewage should be properly treated to make the produced water reach the secondary oil recovery or national discharge requirements. According to the existence form and characteristics of oily substances in water, there are many treatment methods for oily wastewater [ 2 - 4] , such as adsorption, electrochemical, flocculation, coagulation-ultrafiltration. Bentonite is a clay mineral with montmorillonite as its main component [5] . Because of its special water absorption, water plasticity, cohesiveness and strong ion exchange, it can absorb oil from water. It is a good Oily wastewater purification agent. In this experiment, sodium bentonite prepared by suspension method was used as the material, dissolved oil was used as the target pollutant, and the adsorption behavior of dissolved oil on sodium bentonite was studied. The chemical behavior in the adsorption process was controlled by controlling the main influencing factors in the adsorption process. Analysis, determine the best process parameters, provide a theoretical basis for the practical application of the project. First, the experimental part (1) Reagents and instruments Bentonite, produced by Shanghai Sihewei Chemical Co., Ltd.; n-hexane, sodium carbonate, sodium hydroxide, hydrochloric acid, etc. are all analytically pure. FU•HUA type constant temperature magnetic stirrer; low speed desktop centrifuge; pHS-2C acidity meter; THZ-82 type air bath constant temperature oscillator; UV-9200 type ultraviolet/visible spectrophotometer, Japan Shimadzu XRD-6000 type X-ray powder diffractometer. (2) Preparation of sodium bentonite [6] Weigh 40g of natural bentonite ore powder, add Na 2 CO 3 solution in a proportion of 25% to make a slurry, adjust the pH value of the slurry to 9, heat, control the temperature at about 90 °C, and stir the reaction for 4 hours. After the reaction is completed, a part of the sodium-based soil glue is separated, dried, and ground through a 100 mesh sieve to obtain a sodium bentonite. (3) Basic performance test of bentonite The cation exchange capacity (CEC), expansion ratio, gelatinous price, blue absorption amount and XRD structure performance were analyzed for sodium bentonite and original soil, respectively. For the specific method, refer to the literature [6] . (4) Configuration of oily wastewater Refer to Tolls [7] and other experimental equipment for determining the solubility of alkanes, first add ultrapure water (resistivity ≥ 18MΩ • cm), then add a thin layer of 35 # diesel on the water phase, dissolve under magnetic stirring Adjust the speed of magnetic stirring so that the depth of the vortex is less than 2cm to prevent the formation of small droplets. After 48h, the solution reaches equilibrium, and the liquid is divided and used. (5) Adsorption experiment Certain amount of sodium bentonite in a glass stoppered centrifuge tube, was added 50mL of an oil solution of known concentration, is sealed by a spin cap, wrapped in a layer of aluminum foil on a shaker until the temperature oscillation adsorption equilibrium in the set Under the experimental conditions, the mixed solution was centrifuged at 3000 r/rain for 20 min. The supernatant was extracted with n-hexane, and the absorbance was measured at 225 nm by an ultraviolet spectrophotometer to calculate the adsorption amount and the degreasing rate. Second, the results and discussion (1) Performance test of sodium bentonite 1. Basic properties of sodium bentonite: The basic properties of the original bentonite and sodium bentonite are shown in Table 1. The results in Table 1 show that after sodium modification, the cation exchange capacity (CEC), expansion ratio and blue absorption amount of the bentonite increased by 1.175 times, 4.218 times and 1.75 times, respectively, and the gelatin price is about four quarters of the original soil. First, the cation exchangeability, swelling property of sodium bentonite and dispersibility in an aqueous medium are remarkably improved. This indicates that the surface properties and interlayer structure of bentonite modified by sodium modification will increase its adsorption selectivity and adsorption performance [8] . 2. X-ray diffraction analysis (XRD) of sodium bentonite: The results of X-ray diffraction (XRD) analysis of bentonite are shown in Fig. 1. The interlayer spacing of the bentonite original soil is 1.527 nm, which is equivalent to the sum of the montmorillonite structure layer (0.961 nm) and the thickness of the two layers of adsorbed water molecules, indicating that the original soil is calcium-based bentonite [9] . After sodium modification, the main diffraction peak shifted to a large angle, and the bottom spacing decreased to 1.241 nm. It is indicated that the calcium cations in the inter-layer of the original calcium-based bentonite have been replaced by sodium ions with smaller hydration radius, and the calcium-based bentonite is modified into sodium-based bentonite [10] . (II) Test of adsorption of oily wastewater by sodium bentonite 1. The effect of dosage on adsorption: at a temperature of 20 ° C, an adsorption time of 60 min and an oily wastewater concentration of 156 mg / L, the amount of bentonite is lg / L, 2g / L, 3g / L, 4g /L, 5g/L, 6g/L, do the adsorption test, the test results are shown in Figure 2. It can be seen from Fig. 2 that with the increase of dosage, the adsorption effect is obviously enhanced. When the dosage is 3.0g/L, the adsorption effect reaches about 55%, but when the dosage is increased, the adsorption is basically When the saturation is reached, the degreasing rate is basically unchanged, and the adsorption load starts to decrease. With the increase of the amount of bentonite, the total amount of cation exchange of bentonite also increases, while the negative charge of bentonite surface decreases, the positive charge increases, and the effect of adsorption and degreasing increases greatly. When the saturated cation exchange amount is reached, the oil is adsorbed and degreased. The effect remains basically the same. In order to achieve a better adsorption effect, the appropriate amount of bentonite must be selected to maximize the removal rate and adsorption load. Therefore, the appropriate amount of bentonite is selected to be 2.5 g/L. 2, the effect of adsorption time on the adsorption effect: in the case of the amount of adsorbent is 2.5g / L, the concentration of oily wastewater is 156mg / L, the initial pH of the solution is 7.0 and the temperature is 20 ° C, change the adsorption time, do a group Adsorption experiments, the experimental results are shown in Figure 3. It can be seen from Fig. 3 that the adsorption of oil by sodium bentonite has been increasing with the increase of adsorption time until it reaches the saturation stage. When the adsorption time is 60 min, the removal rate of oil in the solution is 58.4%; after the adsorption time exceeds 60 min, the adsorption effect does not change much, and it almost approaches the saturation stage, indicating that the adsorption has reached equilibrium. The reason for this phenomenon may be that the initial rapid adsorption is a surface action, and the adsorption rate is relatively fast; the subsequent slow adsorption is a process of migration and diffusion of organic pollutants into the pores of bentonite, and the adsorption rate is relatively slow. 3, the effect of the pH value of the solution on the adsorption effect: in the case of temperature 20 ° C, bentonite dosage 2.5g / L, adsorption time 60mm and oily wastewater concentration 156mg / L, change the pH value of the solution, do adsorption test, test results see Figure 4. As can be seen from Figure 4, as the initial pH of the solution increases, the adsorption rate of sodium bentonite to oil increases. When the pH value is 5.04, the oil absorption rate is the highest; when the solution pH is >5.04, the oil absorption rate is obviously decreased. The reason for the analysis may be because, under strong acidic conditions, H+ can neutralize the negative charge layer on the surface of the oil particles, destroying its stability and enhancing the degreasing effect; under weakly acidic conditions, H+ can be layered to some extent. The sodium ion exchange reaction [9] changes its own properties and affects the degreasing effect. 4. Adsorption isotherm curve: The isothermal adsorption curve is obtained when the oil is adsorbed in the modified bentonite and the original soil at a temperature of 1 to 30 ° C. Figure 5 is an isotherm adsorption curve of two bentonites at 20 °C. As the equilibrium concentration of oil increases, the equilibrium adsorption amount increases, and the adsorption amount of sodium-modified bentonite is significantly higher than that of the original soil. The Langmuir and Freundlich isotherms were used to regress the measured isotherms. The parameters of the Langmuir and Freundlich isotherms are shown in Table 2. It can be seen from Table 2 that the regression results show a good linearity, indicating that the Langmuir isotherm equation and the Freundlich isotherm equation can well describe the adsorption of bentonite on oil. The maximum adsorption amount Q0, adsorption constant KF and other constants related to the adsorption amount decrease with the increase of the adsorption temperature, and the n value is greater than 1, indicating that the adsorption of oil on bentonite is easy. Third, the conclusion (1) Sodium bentonite prepared by suspension method. Various characterization data indicate that sodium ions have entered the interlayer structure of bentonite, and the interlayer spacing has changed, which is beneficial to the improvement of adsorption performance. (2) The effects of various factors on the adsorption efficiency of sodium-bearing bentonite adsorbing oily wastewater were investigated by single factor experiment. The optimal adsorption conditions were as follows: the adsorbent dosage was 2.5g/L, the pH value was about 5, and the adsorption time was 60min. (3) The relationship between the equilibrium adsorption amount Q and the equilibrium concentration C is in accordance with the Frettendlich and Langmuir isotherm adsorption equations. references [1] Yang Yunxia, ​​Zhang Xiaojian. Current status and technical development of reclaimed water treatment in China's oilfields [J]. Industrial Water Supply and Drainage, 2000, 26 (7): 32-35. [2] Sang Yimin, Li Chuan, He Xuwen, et al. The nature of oily wastewater and its treatment technology [J]. Chemical Environmental Protection, 2004, 24: 94-97. [3] Long Chuan, Ke Shuizhou, Hong Junming, et al. Research progress in oily wastewater treatment technology [J]. Industrial Water Treatment, 2007, 27(8): 4-7. [4] Ma Liyan, Guan Weisheng, Wang Xingang. Experimental study on coagulation-ultrafiltration treatment of oil wastewater[J].Water Treatment Technology,2006,3201):74-76. [5]LI Bo,REN Ruichen,LI Caixia.Preparation of pellets and composite binders by orthogonal experiment[J].Liaoning University of Engineering and Technology,2007,27(增):292-293. . [6] before the new leaves, Zhan, Zhao Yuning modified bentonite Experimental Study Petrochemical Oil Wastewater [J] non-metallic mineral processing, 2004,27 (2): 41-43. [7] Sun Hongliang, Zhu Lizhong. Preparation, Characterization and Adsorption Properties of Bentonite Nanocomposites Ming. Journal of Inorganic Chemistry, 2007, 23(7): 1148-1152. [9]Hou Li,Yi Facheng,Zhou Jiarong.Study on sodium modification of calcium bentonite[J].China Mining,2006,15(12):77-79. [10]Qiu Jun,Zhang Yangui,Lü Xianjun.Study on the Sodiumation and Performance Differences of Two Different Crystal Characteristics of Montmorillonite[J].åŒ–å·¥çŸ¿ç‰©ä¸ŽåŠ å·¥,2007,10:16-19.
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