RESULTS OF PILOT TESTS OF THE VSEP TECHNOLOGY ON THE EXAMPLE OF PURIFICATION OF CONTAMINATED ACID WASHING WATERS BY NANOFILTRATION

Shown are the results of a series of pilot tests for the purifi cation of waste (contaminated) acidic wash water formed during the production of graphite by the leaching method. The tests were carried out in laboratory and pilot modes (on-site) on the “LP” series machine. Purifi cation was simulated using nanofi ltration membranes using VSEP technology. This technology of vibro- membrane fi ltration makes it possible to purify such waters without preliminary purifi cation and the use of reagents (antiscalant) with a %Recovery more than 90 %. The mechanism for choosing the optimal sheet polymer membrane and the mechanism for determining the best working pressure are shown. Concentration series were carried out to determine the stability of the process and the duration of the fl ushing interval. The test results allow the design of an industrial water purifi cation system.

Surface Pretreatments of AA5083 Aluminum Alloy with Enhanced Corrosion Protection for Cerium-Based Conversion Coatings Application: Combined Experimental and Computational Analysis

The effects of surface pretreatments on the cerium-based conversion coating applied on an AA5083 aluminum alloy were investigated using a combination of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), polarization testing, and electrochemical impedance spectroscopy. Two steps of pretreatments containing acidic or alkaline solutions were applied to the surface to study the effects of surface pretreatments. Among the pretreated samples, the sample prepared by the pretreatment of the alkaline solution then acid washing presented higher corrosion protection (~3 orders of magnitude higher than the sample without pretreatment). This pretreatment provided a more active surface for the deposition of the cerium layer and provided a more suitable substrate for film formation, and made a more uniform film. The surface morphology of samples confirmed that the best surface coverage was presented by alkaline solution then acid washing pretreatment. The presence of cerium in the (EDS) analysis demonstrated that pretreatment with the alkaline solution then acid washing resulted in a higher deposition of the cerium layer on the aluminum surface. After selecting the best surface pretreatment, various deposition times of cerium baths were investigated. The best deposition time was achieved at 10 min, and after this critical time, a cracked film formed on the surface that could not be protective. The corrosion resistance of cerium-based conversion coatings obtained by electrochemical tests were used for training three computational techniques (artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), and support vector machine regression (SVMR)) based on Pretreatment-1 (acidic or alkaline cleaning: pH (1)), Pretreatment-2 (acidic or alkaline cleaning: pH (2)), and deposition time in the cerium bath as an input. Various statistical criteria showed that the ANFIS model (R2 = 0.99, MSE = 48.83, and MAE = 3.49) could forecast the corrosion behavior of a cerium-based conversion coating more accurately than other models. Finally, due to the robust performance of ANFIS in modeling, the effect of each parameter was studied.

Pyrolysis kinetic analysis of sequential extract residues from Hefeng sub-bituminous coal based on Coats-Redfern method

Sequential extract residues (Ri, i=1, 2, 3, 4, 5) were obtained from Hefeng acid-washing coal (HFAC) by petroleum ether, carbon disulfide, methanol, acetone and isometric carbon disulfide/acetone mixture, sequentially. Pyrolysis behavior of the samples was carried out using thermogravimetry analysis. Coats-Redfern method with different reaction order was used to analyze the pyrolysis kinetic of each sample, and the kinetic parameters, including correlation coefficient (R2), activation energy (E), pre-exponential factor (A), were calculated. Results showed that the weight loss of extract residues was higher than HFAC, and pyrolysis behavior varies greatly for residues, which may be due to unstable structure after extraction. From conversion-temperature (α-T) curves, pyrolysis process was divided into three stages: low-temperature stage (150-350 oC), medium temperature stage (350-550 oC) and high temperature stage (550-950 oC). And the medium temperature stage made great contribution to the process of pyrolysis, which was dominated by depolymerization and decomposition reaction, and the effect of kinetic fitting to this stage is better, with R2 higher than 0.95. Relationship between kinetic parameters and reaction order showed that swelling effect might be an important reason for the discrepancy of E for each sample in the process of pyrolysis. And Ln(A)-E relationship has a great significance to predict E and the A under higher reaction order.

Significance of Acid Washing after Biooxidation of Sulfides in Sequential Biotreatment of Double Refractory Gold Ore from the Syama Mine, Mali

Environmentally friendly pretreatment of double refractory gold ores (DRGO) to improve gold recovery without emitting pollutant gas is challenging. Sequential biotreatment, including iron-oxidizing microorganisms to decompose sulfides, followed by the enzymatic decomposition of carbonaceous matter, was recently developed. The effect of acid washing by 1 M HCl for 24 h between two bioprocesses was evaluated using a real double refractory gold ore from the Syama mines, Mali, which includes 24 g/t of Au and 5.27 wt % of carbon with a relatively higher graphitic degree. The addition of the acid washing process significantly improved gold recovery by cyanidation to yield to 84.9 ± 0.7% from 64.4 ± 9.2% (n = 2). The positive effects of acid washing can be explained by chemical alteration of carbonaceous matter to facilitate the accessibility for lignin peroxidase (LiP) and manganese peroxidase (MnP) in cell-free spent medium (CFSM), although the agglomeration was enhanced by an acid attack to structural Fe(III) in clay minerals. Sequential treatment of DRGO basically consists of the oxidative dissolution of sulfides and the degradation of carbonaceous matter prior to the extraction of gold; however, the details should be modified depending on the elemental and mineralogical compositions and the graphitic degree of carbonaceous matter.

Methods to Improve nZVI Adsorbance on Silicates Surface for Nitrate Reduction

<p>Efforts to remove excess nitrate in the groundwater typically involves expensive ion-exchange membranes or slow reacting bio-reactors. Nano-sized zero valent iron (nZVI) has been used successfully to reduce nitrate into ammonia in various sites in USA and Europe. However, nZVI has a number of major setbacks associated with it, namely the tendency to agglomerate due to magnetic properties, and the possible toxicity due to the nano-sized material. To circumvent these two setbacks, nZVI could be adsorbed onto solid support. In this research, geothermal sediment microsilicate 600 (Misi) was utilised as a support. Initial results suggested that Misi has potential as a support for nZVI, however modifications were required to improve the adsorbance of nZVI onto Misi surface. Calcination, activation, acid wash and iron oxyhydroxide coating were used as surface modifications for Misi. It was found that the two most important modifications for nZVI adsorption was calcination at either 400 or 600 °C and acid washing in 5.6 M HCl. Equipped with this knowledge, other silica and silicates were also used to adsorb nZVI. For pure silica surfaces, 3-APTES and 3-TPTMS ligands and pore enlarging methods of calcination of porogen and salt wash were also used. nZVI was not able to be fully adsorbed on pure silica surfaces. Four other silicates were examined: Rice husk ash, Western Australia silica fume, Mt Piper fly ash, and precipitated aluminium silicate. Of these, only Western Australia silica fume and precipitated aluminium silicate showed potential as nZVI support. Based on the SEM-EDS XRD data of all the silica and silicates, it could be tentatively concluded that nZVI requires an aluminium silicate surface for successful adsorption. Aluminium silicate surfaces typically has an exchangeable cation present, and this cation might play a part in nZVI adsorption. The nZVI/Misi surface was then utilised to reduce nitrate. It was discovered that even though activation and FeOOH did not play a part in nZVI adsorption onto Misi surface, these two steps were important in reduction of nitrate, as the presence of activation and FeOOH increase the reduction of nitrate significantly within 60 minutes. The Misi-supported nZVI were also shown to be more stable in dispersion, and less agglomerated as shown in a sand column experiment.</p>

Methods to Improve nZVI Adsorbance on Silicates Surface for Nitrate Reduction

<p>Efforts to remove excess nitrate in the groundwater typically involves expensive ion-exchange membranes or slow reacting bio-reactors. Nano-sized zero valent iron (nZVI) has been used successfully to reduce nitrate into ammonia in various sites in USA and Europe. However, nZVI has a number of major setbacks associated with it, namely the tendency to agglomerate due to magnetic properties, and the possible toxicity due to the nano-sized material. To circumvent these two setbacks, nZVI could be adsorbed onto solid support. In this research, geothermal sediment microsilicate 600 (Misi) was utilised as a support. Initial results suggested that Misi has potential as a support for nZVI, however modifications were required to improve the adsorbance of nZVI onto Misi surface. Calcination, activation, acid wash and iron oxyhydroxide coating were used as surface modifications for Misi. It was found that the two most important modifications for nZVI adsorption was calcination at either 400 or 600 °C and acid washing in 5.6 M HCl. Equipped with this knowledge, other silica and silicates were also used to adsorb nZVI. For pure silica surfaces, 3-APTES and 3-TPTMS ligands and pore enlarging methods of calcination of porogen and salt wash were also used. nZVI was not able to be fully adsorbed on pure silica surfaces. Four other silicates were examined: Rice husk ash, Western Australia silica fume, Mt Piper fly ash, and precipitated aluminium silicate. Of these, only Western Australia silica fume and precipitated aluminium silicate showed potential as nZVI support. Based on the SEM-EDS XRD data of all the silica and silicates, it could be tentatively concluded that nZVI requires an aluminium silicate surface for successful adsorption. Aluminium silicate surfaces typically has an exchangeable cation present, and this cation might play a part in nZVI adsorption. The nZVI/Misi surface was then utilised to reduce nitrate. It was discovered that even though activation and FeOOH did not play a part in nZVI adsorption onto Misi surface, these two steps were important in reduction of nitrate, as the presence of activation and FeOOH increase the reduction of nitrate significantly within 60 minutes. The Misi-supported nZVI were also shown to be more stable in dispersion, and less agglomerated as shown in a sand column experiment.</p>

Enhanced Removal of Pb from Electrolytic Manganese Anode Slime by Vacuum Carbothermal Reduction

Electrolytic manganese anode slime (EMAS) is produced during the production of electrolytic manganese metal. In this study, a method based on vacuum carbothermal reduction was used for Pb removal in EMAS. A Pb-removal efficiency of 99.85% and MnO purity in EMAS of 97.34 wt.% was obtained for a reduction temperature of 950°C and a carbon mass ratio of 10% for a holding time of 100 min. The dense structure of the EMAS was destroyed, a large number of multidimensional pores and cracks were formed, and the Pd-containing compound was reduced to elemental Pb by the vacuum carbothermal reduction. A recovery efficiency for chemical MnO2 of 36.6% was obtained via preparation from Pd-removed EMAS through the “roasting-pickling disproportionation” process, with an acid washing time of 100 min, acid washing temperature of 70°C, H2SO4 concentration of 0.8 mol/L, liquid-solid mass ratio of 7 mL/g, calcination temperature of 60°C and calcination time of 2.5 h. Moreover, the crystal form of the prepared chemical MnO2 was found to be basically the same as that of electrolytic MnO2, and its specific surface area, micropore volume and discharge capacity were all higher than that of electrolytic MnO2. This study provides a new method for Pd removal and recycling for EMAS.