Renlong Liu

Solidification/stabilization of electrolytic manganese residue using phosphate resource and low-grade MgO/CaO

In this study, P-LGMgO (low-grade MgO and NaH2PO4·2H2O), P-CaO (CaO and NaH2PO4·2H2O), and P-MgCa (low-grade MgO, CaO and NaH2PO4·2H2O) were used for the solidification/stabilization (S/S) of electrolytic manganese residue (EMR). Relevant characteristics such as ammonia nitrogen and manganese stabilization behavior, unconfined compressive strength (UCS), probable S/S mechanisms, and EMR leaching test were investigated. The results demonstrate that using P-LGMgO had higher stabilization efficiency than P-CaO and P-MgCa for the S/S of EMR at the same stabilization agent dose. The stabilization efficiency of ammonia nitrogen and manganese in the EMR were 84.0% and 99.9%, respectively, and the UCS of EMR was 5.1MPa using P-LGMgO process after curing for 28 days when the molar ratio of Mg:P was 5:1 and dose of stabilization agent was 12wt%. In this process, ammonia nitrogen was stabilized by struvite (NH4MgPO4·6H2O), and manganese by bermanite (Mn3(PO4)2(OH)2·4H2O) and pyrochroite (Mn(OH)2). The leaching test results show that the values of all the measured metals on the 28th day were within the permitted level for the GB8978-1996 test suggested by Chinas environmental protection law and the concentration of ammonia nitrogen can be reduced from 504.0mgL(-1) to 76.6mgL(-1).

Microwave-assisted degradation of waste polyethyleneterephthalate (PET) at atmospheric pressure using silicon carbide as power modulator

Degradation of waste PET is an important issue nowadays. Microwave-assisted degradation of waste PET in alcohol was carried out utilizing silicon carbide (SiC) as power modulators. Even at atmospheric pressure, reaction time could be shortened from several hours to 30 min, and the degradation rate was increased by 12%. PET degradation efficiency at atmospheric pressure was up to 96% with amount of SiC 60 g/L under microwave irradiation at 700 W for 30min. As a type of inert and highly reusable power modulators, SiC could improve the transfer efficiency of the microwave energy.

Simultaneous stabilization/solidification of Mn 2+ and NH 4 + -N from electrolytic manganese residue using MgO and different phosphate resource

This study examined simultaneous stabilization and solidification (S/S) of Mn2+ and NH4+-N from electrolytic manganese residue (EMR) using MgO and different phosphate resource. The characteristics of EMR NH4+-N and Mn2+ S/S behavior, S/S mechanisms, leaching test and economic analysis, were investigated. The results show that the S/S efficiency of Mn2+ and NH4+-N could reach 91.58% and 99.98%, respectively, and the pH value is 8.75 when the molar ratio of Mg:P is 3:1 and the dose of PM (MgO and Na3PO4·12H2O) is 8wt%. In this process, Mn2+ could mainly be stabilized in the forms of Mn(H2PO4)2·2H2O, Mn3(PO4)2·3H2O, Mn(OH)2, and MnOOH, and NH4+-N in the form of NH4MgPO4·6H2O. Economic evaluation indicates that using PM process has a lower cost than HPM and HOM process for the S/S of Mn2+ and NH4+-N from EMR at the same stabilization agent dose. Leaching test values of all the measured metals are within the permitted level for the GB8978-1996 test suggested when the dose of PM, HPM and HOM is 8wt%.

Simultaneous removal of ammonia nitrogen and manganese from wastewater using nitrite by electrochemical method

ABSTRACT In this work, nitrite was developed to simultaneously remove manganese and ammonia nitrogen from wastewater by the electrochemical method. The characteristics of electrolytic reaction were observed via cyclic voltammograms. Moreover, the mole ratio of nitrite and ammonia nitrogen, voltage, and initial pH value, which affected the removal efficiency of ammonia nitrogen and manganese, were investigated. The results showed that the concentration of ammonia nitrogen in wastewater could be reduced from 120.2 to 6.0 mg L−1, and manganese could be simultaneously removed from 302.4 to 1.5 mg L−1 at initial pH of 8.0, the mole ratios of nitrite and ammonia nitrogen of 1.5:1, and voltage of 20 V direct current electrolysis for 4.0 h. XRD analysis showed that manganese dioxide was deposited on the anode, and manganese was mainly removed in the form of manganese hydroxide precipitation in the cathode chamber.

Leaching of manganese from electrolytic manganese residue by electro-reduction

ABSTRACT In this study, an improved process for leaching manganese from electrolytic manganese residue (EMR) by electro-reduction was developed. The mechanisms of the electro-reduction leaching were investigated through X-ray diffraction, scanning electron microscopy, X-ray fluorescence, and Brunauer Emmett Teller. The results show that the electric field could change the surface charge distribution of EMR particles, and the high-valent manganese can be reduced by electric field. The leaching efficient of manganese reached 84.1% under the optimal leaching condition: 9.2 wt% H2SO4, current density of 25 mA/cm2, solid-to-liquid ratio of 1:5, and leaching time for 1 h. It is 37.9% higher than that attained without an electric field. Meanwhile, the manganese content in EMR decreased from 2.57% to 0.48%. GRAPHICAL ABSTRACT

Decolorization of methyl orange solution catalyzed by fly ash-H 2 O 2 under microwave irradiation

This study explored the potential use of fly ash from coal as a heterogeneous catalyst in the degradation of azo dye by using H2O2 irradiated by microwave. The effects of various parameters such as fly ash loading, temperature, pH, initial concentration of methyl orange, and dosage of H2O2, and deactivation of catalytic effect of fly ash were studied. The metal oxide compounds in fly ash, such as iron and manganese, can combine with H2O2 to form a Fenton-like reagent and produce hydroxyl radical, which can oxidize persistent organic pollutants into small molecule compounds. Under microwave irradiation, methyl orange (MO) solution, a typical azo dyestuff selected as a model pollutant, was decolorized. For the 100mL 1000mg/L MO solution, the decolorization and COD removal ratios were 99.8% and 80%, respectively, with a pH of 2, 2 grams of fly ash, 1 mL of 30% H2O2, 800 W of microwave power, and an irradiation time of 5 minutes. The negligible homogeneous catalytic action of trace metals leached from the fly ash such as Fe, Mn, and Cu, confirmed the sole heterogeneous catalytic nature of fly ash particles in the cleavage of azo bonds. Fly ash deactivation was found to be <40% in 4 repeated uses.