Research On Technics Of Removing Iron In Oilfield Wastewater

Water is the indispensable resource in human's life and producing activities. And, at the same time, it is the natural byproduct of Petroleum. In the process of oilfield exploiting, there is more and more oilfield wastewater which pollutes the entironment severely. Treating and reinjecting oilfield wastewater is a correct way to develop and use water resource at present. Lately, there are many research and reports about oilfield wastewater treatment, but a few systemic research about how to remove iron in oilfield wastewater. It is easy to make the system polluted and scale if there is too much oil and suspended solid. Especially if the iron exits, it will make the oilfield wastewater more difficult to treat. If the oilfield wastewater with iron is reinjected, the water reinjecting pipeline net will be damaged easily;the stratum will be jammed;and the testing tools will be rusted and blocked. As a result of that, the amount of reinjecting water will decrease and the effect will be weaken. The exploiting of oilfield is affected severely.This paper makes research on the problem that the amount of iron in oilfield wastewater of Gansu Yumen can not meet the needs. The technicology of flocculating precipitation combined with filtration is adopted. The optimum condition is concluded by cross experiment and single factor optimizing experiment as follows: PAC 5mg/L, pH 7.5, water temperature 25°C, time of stirring 10min, time of precipitation 15min. The rate of Fe³⁺removing is 97.44% under this condition.Flocculation is preferable for removing Fe³⁺, but not so good for removing Fe²⁺, so the oxidation experiment was carried on. The oxidant NaClO was chosen as the optimal oxidant. When it was used, the rate of Fe²⁺ removing achieved to 78.57%, the rate of total iron increased from 57.10% to 80.44% compared to the condition that NaClO was not used. Contact oxidation filtration was adopted as the subsequent treating technics.Four filter stuff such as quartz sand, high quality manganese sand, silicon carbide and fibre balls were studied by the way of antitheses. It is concluded that silicon carbide is the most suitable for the oilfield wastewater. Synchronously, thecontrol parameter of removing iron by Contact oxidation filtration is delivered as follows: dissolvable oxygen(DO)> 1.23mg/L, filter speed 4m/h, pH 7.5;Under this condition, the equation that related to Fe2+ concentration and filter layer' depth was deduced as [Fe2+]=[Fe2+]o. e"629L. The concentration of Fe2+at any filter layer' depth can be inferred in terms of [Fe2+]o and that equation.In order to make iron concentration in discharge water stable and standard, the double layer filter of silicon carbide and tryma shells was introduced. The total iron in discharge water was 0.42mg/L. It can meet the criterion that iron concentration in reinjecting water should be no high than 0.5mg/L.The experimentation indicated that it is totally feasible to decrease iron concentration of Yumen Oilfield wastewater by this technic. The iron in treated water can meet the criterion. The quality of reinjecting water is ensured and the production of oil extraction in oilfield was guaranteed.