Oxidation rate in the preparation of polyferric sulfate coagulant

The oxidation rate of ferrous sulfate was investigated in the preparation of polyferric sulfate(PFS) coagulant. It was proved that this reaction is zero order with respect to Fe2+, first order with respect to NO2(g) and first order with respect to the interface area between gas phase and liquid phase. If the partial pressure of NO2(g) in gas phase is increased or the interface area is increased, the time needed to complete the reaction will be decreased.

Synthesis, characterization, and property test of crystalline polyferric sulfate adsorbent used in treatment of contaminated water with a high As(Ⅲ) content

A crystalline polyferric sulfate(PFS) adsorbent was synthesized by oxidizing and precipitating ferrous ions in air atmospheric conditions. The morphology, structure, specific surface area(SSA), and adsorptive efficacy of the adsorbent to As(Ⅲ) were characterized by scanning electron microscope(SEM) and transmission electron microscopy(TEM) images, X-ray diffraction(XRD) patterns, Fourier-transform infrared(FTIR) spectra, BET SSA analyses, and adsorption experiments. The adsorbent showed a near-spherical aggregate structure and had good crystallinity. A significant amount of α-goethite co-precipitated with PFS in the case of the initial ferrous concentration of 1 mol/L and increased SSA of the adsorbent. The stability region of ferric compounds in the process was drawn and applied to analyze the iron behavior during the synthesis. The adsorption of As(Ⅲ) in high As(Ⅲ)-containing solutions fitted the Langmuir isotherm model adequately. The absorbent with co-precipitation of α-goethite showed good adsorbability for As(Ⅲ) and good filtering performance in the high As(Ⅲ)-containing solution of 10–100 mg/L under acidic, neutral, and alkaline conditions(pH 2.09–9.01). After the adsorption process, the stability of the residues bearing As(Ⅲ) was evaluated by toxic characteristic leaching procedure(TCLP) tests. The results indicated that the residues were extremely stable, and the concentrations of arsenic in the leaching solutions were less than 0.01 mg/L.

Groundwater arsenic removal by coagulation using ferric(Ⅲ)sulfate and polyferric sulfate: A comparative and mechanistic study

Elevated arsenic（As） in groundwater poses a great threat to human health. Coagulation using mono- and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric（III） sulfate（FS） and polyferric sulfate（PFS）performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5 mg/L Ca（ClO）_2. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water（〈 10 μg/L） was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure（XANES） and As k-edge extended X-ray absorption fine structure（EXAFS） analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As（0.9 μg/L-0.487 mg/L）than the US EPA regulatory limit（5 mg/L）. Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water.

Pretreatment of Diosgenin Wastewater Using Polyferric Sulfate and Cationic Polyacrylamide

Coagulation-flocculation process was applied in the pretreatment of diosgenin wastewater.Polyferric sulfate was used as primary coagulant and a cationic polyacrylamide （CPAM） was used as coagulant aid.Using jar test procedure,the influence of the main operating parameters,such as effluent pH and coagulant dosage in the coagulation performance was investigated.The effective pH was found to be in the range of 6.5-8.0 and coagulant dosage was 100 mg/L.Under the optimal conditions,15% chemical oxygen demand （COD） removal efficiency was achieved and the residual turbidity was less than 20 NTU.The presence of CPAM substantially promoted the reduction of residual turbidity with the appropriate CPAM dosage in the range of 2-5 mg/L.

Properties and coagulation mechanisms of polyferric silicate sulfate with high concentration

Polyferric silicate sulfate （PFSS） with high concentration was prepared using the composite-poly method. The coagulation properties and mechanisms of this new complex were probed using TEM, Fe-Ferron timed complex-colorimetric method, and infrared spectrum method. The results showed that the flocculating effect of polyferric silicate sulfate had an advantage over polyferric sulfate （PFS）, as the optimum coagulation effect could be obtained when the Si/Fe mole ratio was 0.75 in accordance with its macrostructure of PFSS. According to the Fe-Ferron timed complex-colorimetric method, the Si species was mainly Sic, whereas, the Fe species were Fea and Fec in the copolymerization system. The infrared spectra indicated that the structure of these new flocculants was formed by polymers, mainly by olation, which was different from polyferric sulfate, and the vibration of M-OH-M of around 1100 cm^-1, also proved that there existed Fe-OH-Fe and its polymers in some forms.

Properties of polyferric-silicate-sulfate(PFSS) coagulant

Polyferric\|silicate\|sulfate(PFSS),as a new type of coagulant,was prepared by using sodium silicate, sulfuric acid and ferric sulfate as materials.The zeta potential of hydrolyzate of PFSS under different pH values was investigated.The effects of Fe/SiO\-2 molar ratio and dosage of PFSS on turbidity removal were studied. The relation between the optimum coagulation pH range and Fe/SiO\-2 molar ratio was found and the coagulation mechanism of PFSS was discussed.The experimental results showed that Fe/SiO\-2 molar ratio has an effect on the zeta potential of hydrolyzate, the coagulation performance and the optimum coagulation pH range of PFSS and that PFSS gives the best turbidity removal effect when its Fe/SiO\-2 molar ratio was 1.5.

Preparation of PFS coagulant by sectionalized reactor

The oxidation rate of ferrous sulfate is investigated for the preparation of polyferric sulfate(PFS) coagulant. It is proved that this reaction is zero order with respect to Fe 2+ , first order with respect to NO 2(g), and first order with respect to the interface area between gas phase and liquid phase. According to this mechanism, sectionalized reactor(SR) is used in place of traditional reactor(TR), and the liquid of reaction mixture is recycled by pump. As a result, not only the flow path of reaction liquid is prolonged, but also gas liquid contact area enlarged, and the reaction distinctly accelerated, compared with traditional reactor. The effects of parameters including temperature, acidity and others on the reaction rate are also discussed.