Study On Adsorption Properties Of Calcium And Magnesium Ions In Oil Wastewater With Modified Sawdust

Oilfield wastewater is produced during oil exploitation and production process, such as produced water in multipurpose station, backwater from flushing fluid, discharge water out of well-drilling and so on. In the meanwhile, substantial water is produced from oil wells at later stage of oilfield development, therefore, in view of pressure-up keeping, plenty of water will be injected into underground. Water produced out of oil wells is disposed and then is reinjected into underground. On the one hand, formation pressure will be kept, production rate is maintained. On the other hand, the quality of sewage discharge will decline. There exists the balance between production and injection. It is of vital industrial and environmental consequence.At present, a large number of oil wastewater treatment technology have the large management process, large investment, poor water quality, which contains high degree of mineralization leading to the growing trend of accumulation of scale, the poor adaptability in a mixture of formation water, logging the affusion well and the water having been treated is far from the basic requirements of water injection, so re-injection process is difficult because of the severe accumulation of scale and the water have to efflux, not only wastes water but also pollutes the environment . Therefore, how to decrease the salinity is this article aim at.In order to remove calcium and magnesium ions of the oilfield wastewater mineralization, sawdust, a relatively abundant and inexpensive material , is being investigated as an adsorbent in this experiment. After a series of modification, the sawdust has adsorption characteristics to calcium and magnesium ions. By infrared spectra, we know about a sulfuric acid-acid, mercapto-, methyl-, carboxyl and curing ingredients in the structure of the absorbent . To understand this new type of adsorption characteristics, some experiments are made in the static and dynamic adsorption, study the effects on adsorption, including the adsorption time, pH, the amount of the adsorbent, rotation speed, concentration, temperature and so on, determine the optimum adsorption conditions; Study on the sawdust adsorption balance and adsorption kinetics; Explore regeneration of modified sawdust in an effective manner.This experimental study can reach the following conclusions:1. In static conditions(1) The best adsorption time to modified sawdust is 20 min of calcium ion and 15min of magnesium ion.(2) The best pH to modified sawdust adsorption is 6.18 of calcium and magnesium ion.(3) The best rotation speed to modified sawdust adsorption is 200 r/min of calcium ion and magnesium ion.(4) Under the 100mg/L concentration of calcium and magnesium ions in the solution, 0.35g of modified sawdust reached 90.7% f calcium adsorption and 0.4g modified sawdust can reached 89% of magnesium ion adsorption.(5)Under the constant adsorbent and different wastewater concentrations, modified sawdust saturation adsorption is 34.29mg/g of calcium ion and 24.13mg/g of magnesium ion;(6)The best temperature to modified sawdust adsorption is T=31℃of calcium ion and T=43℃of magnesium ion;2.In dynamic conditions(1) In different water flow rate condition, the less flow velocity is, the more contact time, the more breakthrough time, the greater exchange capacity to modified sawdust. The use of low-velocity of the solution makes modified sawdust adsorbent more qualified water;(2) In the same flow rate and different concentration of raw water conditions, with the influent concentration increases, the initial solution concentration is higher, outflow curves slope is greater and the calculated saturation adsorption capacity is also greater. However, as the saturated adsorption time, we must need more adsorption column. So to high concentration of raw water, single-stage filtration column can get less qualified water. In order to make full use of adsorption media, we can consider pretreatment or more series technology according to the actual situation in general.3. Through experimental data on the linear fitting, modified sawdust adsorption mechanism and kinetics have the following conclusions:(1) When using the fist kinetic equation Lagergren fitting, R value shows good correlation, which has reached 0.99, the modified sawdust adsorbing calcium and magnesium ions follow the first equation Lagergren, and the film-proliferation steps is the main control steps for the process of adsorption. When using the second kinetic equation, R value is not very well, which less than 0.9, the modified sawdust adsorbing calcium and magnesium ions doesn't follow the second equation Lagergren.(2) The Langmuir and Fruendlich isotherms are both used to fit the data of modified sawdust adsorpting calcium, and magnesium ions use, the R-value is greater than 0.9, indicating good correlation. Therefore modified sawdust adsorption isotherm follows both Langmuir and Freundlich isotherms.4. Saturated NaCl solution is dealed with the modified sawdust for regeneration. Regeneration of sawdust on the calcium ion adsorption effects (94.4%) much more than the newly modified sawdust adsorption (90.7%), but renewable sawdust on the magnesium ion adsorption only reached 70.2%, far less than the original sawdust newly modified sawdust (89%).Some foreign and domestic resource report that sawdust is generally used to handle with Cu²⁺, Cr²⁺, Cr³⁺, Cd²⁺, Zn²⁺, and other heavy metals. Few report sawdust can adsorb Ca²⁺and Mg²⁺, the experiment uses such a wide variety of sources and cheaper prices sawdust. Sawdust is modified as a new type of adsorbent that adsorbs calcium and magnesium ions. This is a creative point in the article. Because of this, the research results have some reference value, promoting the application of adsorbent to a certain extent.