Basic Research On Preparation Of Highly Dispersed Nano-magnesium Hydroxide By Light Burning Magnesium Powder And Its Application In The Treatment Of NH₃-N Wastewater

The resource utilization of lightly burned magnesium oxide and the efficient treatment of ammonia nitrogen in wastewater are of great significance for the realization of China's resource recycling,energy saving and emission reduction and sustainable development strategies.This paper intends to study the application of mechanochemical method/in-situ surface modification method to transform light burned magnesium hydroxide into high quality and high dispersible nanometer magnesium hydroxide,which can be used to solve the scientific problem of wastewater treatment.At present,researches on ammonia nitrogen treatment mainly are aimed at polluting water sources with ultra-high concentration ammonia nitrogen above 500 ppm or ammonia nitrogen wastewater below 50 ppm.In this paper,high concentration?NH3-N concentration of200mg/L?ammonia nitrogen wastewater was treated,and the prepared highly dispersed nanometer magnesium hydroxide was further used to treat ammonia nitrogen wastewater with a content of200ppm by magnesium ammonium phosphate precipitation method.After experimental study,the optimal process parameters for the preparation of highly dispersed nanometer magnesium hydroxide by mechanochemical method/in situ surface modification method were light fired magnesium powder:distilled water:polyethylene glycol with grinding medium ratio of 1:4:4,grinding speed of 1300 r/min,optimal reaction time of 180 min and dispersant of 1%.Under this condition,the samples were prepared,and the d₅₀ and d₉₀ values were 1.04 and 2.75 respectively.The average grain size was 10.7nm.The sample was analyzed by XRD test and the product was brucite magnesium hydroxide with high crystallinity.Magnesium hydroxide was almost completely hydrated and converted into magnesium hydroxide.It was calculated that the sedimentation rate of the product was V=0.067ml/min,which was significantly reduced compared with the unmodified magnesium hydroxide.SEM tests were carried out on the samples,and the particles were observed to be hexagonal flakes with high integrity,with a thickness of 5¹0nm and good dispersibility.The particle agglomeration was improved compared with the unmodified magnesium hydroxide.This highly dispersed nanometer magnesium hydroxide was used to treat ammonia nitrogen wastewater with a concentration of 200mg/L,and a better ammonia nitrogen removal effect was obtained.The orthogonal experiment was conducted to study the effects of various factors on the removal of ammonia nitrogen from wastewater,and the results were as follows:the addition of phosphoric acid had the largest effect on the removal of ammonia nitrogen followed by the addition of magnesium hydroxide,and the reaction time had little effect,while the mixing time had little effect.The single-factor comparative experimental study determined the optimal reaction parameters of ammonia nitrogen removal effect:when n?P?/n?n?was 0.8,mixing time was 20min,n?Mg?/n?n?was 2.0,and reaction time was 18min,the ultimate residual concentration of ammonia nitrogen was 61mg/L.This experimental study not only has a good removal effect on ammonia nitrogen in wastewater,but also has a simple process and easy realization of process conditions,which reduces the treatment cost and does not produce secondary pollution to the environment,so it has a strong market competitiveness.