Ph Adjusting Agent, Magnesium Hydrogen Phosphate Adsorption Of Ca (oh) <sub> 2 </ Sub> To Deal With Ammonia Wastewater

Magnesium ammonium phosphate (MAP) precipitation method,extensively applied in treating ammonia wastewater of iron and steelmaking, oil refining, fertilizer, chemical industry, ferroalloy glass,fabricate, meat process, feed production and so on, has been developedrapidly. However, there exist some disadvantages, such as high cost, highconsumption of dosage precipitator and alkali, limited disposal way of theprecipitate, and effluent difficult to meet the standards.In magnesium hydrogen phosphate (MHP) adsorption process,ammonia was removed with MHP which could be recycled through thepyrogenation of the adsorption product MAP. Problems of chemicalcomsuption and disposal of MAP precipitates in MAP precipitationmethod were solved. Chemical cost was further reduced compared NaOHthrough using CaO to adjust pH. Moreover, pyrogenation product NH₃could be recovered as ammonia with high purity. The effluent could befurther treated by zeolite.The main conclusions and findings could be summarized as follows:Effects of pH, temperature, initial NH₄⁺ concentration on NH₄⁺adsorption with MHP were studied for NH₄⁺ wastewater with low andmiddle concentration. Process conditions were optimized: 20～25℃, pH=9 in NH₄Cl, 40℃, pH=9 in (NH₄)₂SO₄, 25～30℃, pH=13.5 in(NH₄)₂CO₃. NH₄⁺ adsorption capacity of MHP raised with the increase ofNH₄⁺ concentration.Effects of mole ratios of MHP, CaO and NH₄⁺ on NH₄⁺ adsorptionwith MHP were investigated for NH₄⁺ wastewater with highconcentration. Process conditions were optimized: initial NH₄⁺ 3.6g/L,n(MHP):n(NH₄⁺)=2:1, CaO 6g/L in NH₄Cl, initial NH₄⁺ 8g/L,n(MHP):n(NH₄⁺)=2.5:1, CaO 13.3g/L in (NH₄)₂SO₄, initial NH₄⁺3.6g/L, n(MHP):n(NH₄⁺)=1:1, CaO 6g/L in (NH₄)₂CO₃. Ammonialremoval rate were 82.8％, 50.5％and 25％in NH₄Cl, (NH₄)₂SO₄ and(NH₄)₂CO₃ wastewater respectively.Circulationg capacity of MHP in 900mg/L and 3.6g/L NH₄⁺ wastewater fell with the increase of adsorption times while that of MHPin 10g/L NH₄⁺ wastewater was stable.Thermodynamics was investigated for Mg²⁺-PO₄^3--NH₄⁺-H⁺-H₂Osystem. The distribution of phosphate ions of different pH was calculated.lg[Mg²⁺]～lg[NH₄⁺], lg[NH₄⁺]～pH and lg[Mg²⁺]～pH diagrams fordissolution-precipitation equilibrium of Mg²⁺-PO₄^3--NH₄⁺-H⁺-H₂O systemwere drawn.When pH was 7.0～8.0, Na-zeolite modified by natural zeolite couldadsorb NH₄⁺ in wastewater treated by MHP process. NH₄⁺ adsorptioncapaciry was up to 9.67mg/g as well as NH₄⁺ removal rate 96.7% andresidual concentration 33.48mg/L in 1000mg/L NH₄⁺ wastewater.Zeoliteadsorption equilibrium could be described by Langmuir isotherm withR²=0.977. The kinetics curve showed the characteristics of rapidadsorption and slow equilibrium. The ion exchange of zeolite adsorbingNH₄⁺ could be accorded with intraparticle diffusion model.