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Ca (OH) _2 pH adjusting agent magnesium hydrogen phosphate adsorption Ammonia Nitrogen in Wastewater

Author: WangZuo
Tutor: ZhouKangGen
School: Central South University
Course: Environmental Engineering
Keywords: Magnesium hydrogen phosphate (MHP) pyrogenation ammonia wastewater
CLC: X703
Type: Master's thesis
Year: 2007
Downloads: 198
Quote: 2
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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 (NH42SO4, 25~30℃, pH=13.5 in(NH42CO3. 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 (NH42SO4, initial NH4+3.6g/L, n(MHP):n(NH4+)=1:1, CaO 6g/L in (NH42CO3. Ammonialremoval rate were 82.8%, 50.5%and 25%in NH4Cl, (NH42SO4 and(NH42CO3 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+-PO43--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+-PO43--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.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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