Efficiency Of Removing Ammonium/Manganese From Groundwater By Ni-Mn Co-Oxide Filter Material

In the process of protecting water sources and controlling pollution sources,micropollutants caused by groundwater sources,such as ammonium（NH₄⁺-N）and manganese(Mn²⁺),should also be given attention.These pollutants are prevalent in drinking water sources in China.Recently,the catalytic oxidation of NH₄⁺-N and Mn²⁺by manganese-based composite oxides（MnOx）has gained attention as an alternative to traditional biological filtration methods that rely on the microbial transformation or chemical oxidation mechanisms.In contrast,Mn Ox mainly achieves the continuous removal of NH₄⁺-N and Mn²⁺through chemical catalytic oxidation.Manganese oxide can be doped with elements or substances by physical,chemical,or electrochemical methods to improve its performance,increase the utilization rate of active substances,and optimize its catalytic or adsorption performance.This study focused on investigating the influence of nickel on the pollutant removal performance of Chemical-Oxidation,Natural-Oxidation and Artificial-Coating manganese oxide filter materials and their substructure and properties,including surface properties.The study utilized research methods such as X-ray diffraction（XRD）,field emission scanning electron microscope（FE-SEM）,infrared spectrometer（FTIR）,photoelectron spectroscopy（XPS）,and inductively coupled plasma mass spectrometry（ICP）to investigate the influence of nickel metal ion doping on the physical and chemical properties of bischofite and its performance in removing ammonium and manganese from manganese oxide filter media.The major results of this study are as follows:（1）According to the pilot experiment of preparing filter material by Chemical-Oxidation method and Natural-Oxidation method,under the examined Ni/Mn ratio conditions（Ni/Mn=0,2.5%,5.0%or 0,5.0%,10.0%）,it was found that an appropriate Ni/Mn ratio could slightly shorten the start-up period of Mn Ox filter material,enhance the stability of removing ammonium/manganese during the start-up period,and improve the efficiency of pollutant removal along the depth of the filter column.The addition of Ni during the Artificial-Coating filter material start-up process could accelerate the start-up speed of ammonium removal,and increase the efficiency of removing ammonia/manganese along the depth of the filter column.Artificial-Coating filter material has the best performance in manganese removal ability,which can reach up to7.5mg/L under experimental conditions;Chemical-Oxidation method has the fastest start-up speed and could be done within 10 days.The ammonium removal performance of the three filter columns were mainly limited by the dissolved oxygen concentration,and there is only a difference in the start-up speed.There is no significant difference in the maximum ammonium removal capacity.（2）According to the characterization analysis of filter materials,under the influence of Ni,more Mn Ox particles were formed on the surface of the filter material when removing pollutants.The surfaces of Chemical-Oxidation,Natural-Oxidation,and Artificial-Coating filter material have shown wrinkled or clustered/nano-flower-shaped structures.These structures along with their uniformly distributed interlayer pores support the infiltration and binding of pollutants.As a result,they facilitate absorption-catalytic collaborative removal of pollutants.According to XRD and XPS characterization analysis,the increase in the proportion of Ni added will reduce the grain size and increase the dispersibility.Mn Ox formed by Ni participation occupies the lattice space of manganese oxide,increases the defect of the lattice,and causes distortion,which also leads to a decrease in grain size.（3）Ni-Mn co-oxide has high catalytic activity.The appropriate Ni/Mn ratio could improve the crystallinity of manganese oxide and accelerate the maturation of filter material,but does not change its amorphous characteristics.Mn OOH is an important component of manganese oxide filter material to remove ammonium/manganese,and the effect of removing ammonium/manganese is better,while the effect of removing ammonia/manganese by Mn^x+-OH is relatively poor.The-OH and lattice oxygen content on the surface of Ni-containing manganese oxides are high,and the hydroxyl energy barrier on the surface of metal oxides is reduced after Ni doping,which is conducive to the catalytic reaction.