| To treat the coking wastewater which contains high concentrations of volatile phenols, ammonia-nitrogen, a two step method of manganese ore oxidation and magnesium ammonium phosphate (struvite) precipitation was proposed in this study. Firstly, the pH value was adjusted to acidity using phosphoric acid and sulphuric acid, volatile phenols and other reducing contaminations in the coking wastewater were removed by manganese oxides accoding to its strong oxidation in acidic condition. And the concentration of CODCr was decreased. Secondly, the magnesia was added to the above coking wastewater treated by manganese ore to perform the precipitation experiment, then ammonia-nitrogen and phosphate will be removed and recovered.Adjusted pH value of 10L coking wastewater to 1.2, then acidic wastewater was oxidized by manganese ore. The removal efficiencies of volatile phenols and CODCr were 99% and 70%; then magnesia was added to the above coking wastewater treated by manganese ore, ammonia-nitrogen was removed and recovered in the form of magnesium ammonium phosphate at a solid-liquid ratio of 18 g/L after 24 hours stirring. The removal efficiency of ammonia-nitrogen was 90.1% and pH value of wastewater increased to 9.4. The characterization of the crystallized product by X-ray diffraction (XRD) and transmission electron microscope (TEM) indicated that the struvite formed and grew on the surface of the magnesia particles.Through the static experiment on oxidation of 3 substituted phenols by manganese ore, substituted phenols reduced in the following order: 4-chlorophenol > 4-methylphenol > 4-nitrophenol. When para substituents on the benzene ring is electron-donating groups, substituted phenols are oxidized by manganese ore more easily according to the instability of substituted phenols increased. When para substituents is electron withdrawing group, substituted phenols are difficult to oxidize by manganese ore according to the stability of substituted phenols increased.
|
PDF Full Text Request