Stainless Steel Mesh Cathode Research Articles

Copper–gold ore processing with ion exchange and SART technology

Anglo Asian Mining has developed a 50,000ozAu/yr open pit gold mine at Gedabek in Western Azerbaijan. The deposit at Gedabek is a copper–gold porphyry, comprising both oxide and sulphide ore mineralisation, which is being mined at the rate of about 1 million tons of ore per year. Ore processing is by conventional cyanide heap leaching, which produces a pregnant leach solution (PLS) containing 1–2ppm of gold, together with 1000ppm or more of copper. The PLS is treated by column ion exchange, using Dow’s gold-selective MINIX resin. Loaded resin is stripped with an acidic thiourea solution, from which gold and silver are electrowon on to stainless steel mesh cathodes. Copper concentrations in the leach solutions are controlled by passing part of the PLS flow through a SART process, where the acronym stands for “Sulphidisation, Acidification, Recycling and Thickening”. The product from the SART process is a copper/silver sulphide precipitate, which is thickened, filtered and dried and then sold for copper smelting.

DOW CORNING 1-2577 Conformal Coating as an efficient diffusion material for cathode in the microbial fuel cell

In this study, DOW CORNING 1-2577 Conformal Coating was proposed for the cathode diffusion layer of the microbial fuel cell (MFC). In MFCs, stainless steel mesh cathodes using DOW CORNING 1-2577 Conformal Coating/carbon as the diffusion layer and two poly (dimethylsiloxane) (PDMS)/carbon diffusion layers and carbon cloth cathode with four poly (tetrafluoroethylene) (PTFE) diffusion layers were constructed for comparison. Under the same operational condition, the MFCs with the DOW CORNING 1-2577 Conformal Coating/carbon diffusion layer produced the maximum power density of 1585±52 mW·m−2, compared with those using poly (tetrafluoroethylene) (PTFE) diffusion layers (1421±45 mW·m−2) and poly (dimethylsiloxane) (PDMS)/carbon diffusion layers (1353±49 mW·m−2). The DOW CORNING 1-2577 Conformal Coating could be an alternative for the diffusion layer construction in the MFC due to its remarkable performance and much simple construction procedure.

Degradation of carbon nanotubes in oxygen glow discharges

A study has been undertaken of the degradation of carbon nanotube (CNT)-covered stainless steel mesh cathodes during exposure to low-pressure oxygen glow discharges. Emission spectroscopy and molecular absorption spectroscopy in DC glow discharge and in RF afterglow experiments, as well as morphological evidence, mass spectrometry spectra of condensed oxidation products, and molecular structure models have shown that plasma oxidation favors the production of 2,3 naphthalic anhydride. Absorption spectra taken during plasma oxidation match both literature sources for 2,3 naphthalic anhydride, as well as spectra of a chemical standard. MS data indicate that the only heavy compounds produced during plasma oxidation are poly-cyclic aromatics that can be attributed either directly to 2,3 naphthalic anhydride or to toluene, its major plasma decomposition product. Morphological observations using the scanning electron microscope support the conclusion that the reaction is facilitated by the field enhancement effect that accelerates oxygen ions to the tips of CNTs, where the oxidation takes place. Tests using water vapor show that oxidation is anhydrous, even in the presence of hydrogen.

Enhanced hydrogen generation using a saline catholyte in a two chamber microbial electrolysis cell

High rates of hydrogen gas production were achieved in a two chamber microbial electrolysis cell (MEC) without a catholyte phosphate buffer by using a saline catholyte solution and a cathode constructed around a stainless steel mesh current collector. Using the non-buffered salt solution (68 mM NaCl) produced the highest current density of 131 ± 12 A/m 3, hydrogen yield of 3.2 ± 0.3 mol H 2/mol acetate, and gas production rate of 1.6 ± 0.2 m 3 H 2/m 3·d, compared to MECs with catholytes externally sparged with CO 2 or containing a phosphate buffer. The salinity of the catholyte achieved a high solution conductivity, and therefore the electrode spacing did not appreciably affect performance. The coulombic efficiency with the cathode placed near the membrane separating the chambers was 83 ± 4%, similar to that obtained with the cathode placed more distant from the membrane (84 ± 4%). Using a carbon cloth cathode instead of the stainless steel mesh cathode did not significantly affect performance, with all reactor configurations producing similar performance in terms of total gas volume, COD removal, r cat and overall energy recovery. These results show MEC performance can be improved by using a saline catholyte without pH control.

A method for high throughput bioelectrochemical research based on small scale microbial electrolysis cells

There is great interest in studying exoelectrogenic microorganisms, but existing methods can require expensive electrochemical equipment and specialized reactors. We developed a simple system for conducting high throughput bioelectrochemical research using multiple inexpensive microbial electrolysis cells (MECs) built with commercially available materials and operated using a single power source. MECs were small crimp top serum bottles (5 mL) with a graphite plate anode (92 m 2/m 3) and a cathode of stainless steel (SS) mesh (86 m 2/m 3), graphite plate, SS wire, or platinum wire. The highest volumetric current density (240 A/m 3, applied potential of 0.7 V) was obtained using a SS mesh cathode and a wastewater inoculum (acetate electron donor). Parallel operated MECs (single power source) did not lead to differences in performance compared to non-parallel operated MECs, which can allow for high throughput reactor operation (>1000 reactors) using a single power supply. The utility of this method for cultivating exoelectrogenic microorganisms was demonstrated through comparison of buffer effects on pure ( Geobacter sulfurreducens and Geobacter metallireducens) and mixed cultures. Mixed cultures produced current densities equal to or higher than pure cultures in the different media, and current densities for all cultures were higher using a 50 mM phosphate buffer than a 30 mM bicarbonate buffer. Only the mixed culture was capable of sustained current generation with a 200 mM phosphate buffer. These results demonstrate the usefulness of this inexpensive method for conducting in-depth examinations of pure and mixed exoelectrogenic cultures.

The use and optimization of stainless steel mesh cathodes in microbial electrolysis cells

Microbial electrolysis cells (MECs) provide a high-yield method for producing hydrogen from renewable biomass. One challenge for commercialization of the technology is a low-cost and highly efficient cathode. Stainless steel (SS) is very inexpensive, and cathodes made of this material with high specific surface areas can achieve performance similar to carbon cathodes containing a platinum catalyst in MECs. SS mesh cathodes were examined here as a method to provide a higher surface area material than flat plate electrodes. Cyclic voltammetry tests showed that the electrochemically active surface area of certain sized mesh could be three times larger than a flat sheet. The relative performance of SS mesh in linear sweep voltammetry at low bubble coverages (low current densities) was also consistent with performance on this basis in MEC tests. The best SS mesh size (#60) in MEC tests had a relatively thick wire size (0.02 cm), a medium pore size (0.02 cm), and a specific surface area of 66 m 2/m 3. An applied voltage of 0.9 V produced a high hydrogen recovery (98 ± 4%) and overall energy efficiency (74 ± 4%), with a hydrogen production rate of 2.1 ± 0.3 m 3H 2/m 3d (current density of 8.08 A/m 2, volumetric current density of 188 ± 19 A/m 3). These studies show that SS in mesh format shows great promise for the development of lower cost MEC systems for hydrogen production.

Multi-electrode continuous flow microbial electrolysis cell for biogas production from acetate

Most microbial electrolysis cells (MECs) contain only a single set of electrodes. In order to examine the scalability of a multiple-electrode design, we constructed a 2.5 L MEC containing 8 separate electrode pairs made of graphite fiber brush anodes pre-acclimated for current generation using acetate, and 304 stainless steel mesh cathodes (64 m 2/m 3). Under continuous flow conditions and a one day hydraulic retention time, the maximum current was 181 mA (1.18 A/m 2, cathode surface area; 74 A/m 3) within three days of operation. The maximum hydrogen production (day 3) was 0.53 L/L-d, reaching an energy efficiency relative to electrical energy input of η E = 144%. Current production remained relatively steady (days 3–18), but the gas composition dramatically shifted over time. By day 16, there was little H 2 gas recovered and methane production increased from 0.049 L/L-d (day 3) to 0.118 L/L-d. When considering the energy value of both hydrogen and methane, efficiency relative to electrical input remained above 100% until near the end of the experiment (day 17) when only methane gas was being produced. Our results show that MECs can be scaled up primarily based on cathode surface area, but that hydrogen can be completely consumed in a continuous flow system unless methanogens can be completely eliminated from the system.

Performance evaluation of low cost microbial fuel cell fabricated using earthen pot with biotic and abiotic cathode

An attempt has been made to produce low cost MFC from the commercially available earthen pots in India, without involving any costly membrane. This MFC gave a maximum power output of 16.8 W/m 3 at a Coulombic efficiency (CE) of 31.3% with graphite plate cathode. With stainless steel mesh cathode and KMnO 4 as cathodic electrolyte the power production and CE of 70.48 W/m 3 and 64.5%, respectively, was obtained. The performance of this earthen pot MFC was evaluated with biotic and abiotic cathode. Although, biofilm formation on the cathode is observed to be helpful in enhancing power out put, the thicker biofilm on the cathode showed reduction in power. This MFC demonstrated competitive performance as compared to MFC incorporated with membrane. This low cost MFC, with total production cost of less than 1.0$, as per Indian market, demonstrated its utility as a wastewater treatment and onsite power generation device.

Enhanced denitrification through microbial and steel fuel-cell generated electron transport

Enhancement of nitrate reduction was studied in a two-chambered microbial fuel cell (MFC) and a similar abiotic fuel cell (steel fuel cell or SFC) with an oxidizable steel wool anode and catalyst-free stainless steel mesh cathode. In the MFC and SFC systems, nitrate was reduced in the cathode chamber at 11.4 or 40.0 mg nitrate/L/day, respectively. The MFC utilized petroleum compounds in refinery wastewater as the electron donor and the SFC utilized steel wool as the electron donor. Oxidation of the petroleum compounds in the MFC and steel wool in the SFC caused electron flow from the anode to the cathode, where nitrate was reduced. Nitrate reduction was significantly ( P < 0.001) higher in SFCs with non-sterile groundwater in the cathode chambers and the flow of electrons to the cathode stimulated microbial growth. Our results suggest the both MFC and SFC designs could serve as electron source for nitrate reduction at the cathode. Particularly the SFC could be an innovative low-cost, low-maintenance alternative for in situ remediation of nitrate-contaminated groundwater.

The removal of zinc from liquid streams by electroflotation

The removal of heavy metals from dilute aqueous solutions (in the range of 10 −7–10 −4 mol dm −3) is often not acceptable using classical methods, which do not achieve levels in accordance with environmental quality standards. Electroflotation has certain desirable characteristics, compared to dissolved and dispersed air flotation, particularly in regard to the small bubble size distribution of the process. The aim of this work was to develop an electroflotation (EF)/electrocoagulation (EC) cell to study this combined process and the influence of some relevant parameters/variables, such as collector concentration, tension and current density variation, on the removal of zinc from synthetic solutions containing 20 mg l −1 of the metal. A platinum gore (5 mm) anode and stainless steel mesh cathode were used in the electroflotation cell. The work showed that it was possible to remove zinc by electroflotation, 96% removal being achieved using sodium dodecyl sulfate (SDS) as collector in the stoichiometric ratio 1:3, current density of around 8 mA/cm 2 and an inlet pH of about 7.0.

Electrolytic Preparation of Vanadium(II) Formate in Pilot-Plant Scale Using Stainless Steel Mesh Electrodes: Dissolution of α-Fe2O3/Fe1.6Cr0.4O3 in an Aqueous VII-NTA Complex

The chemical formulations containing strong reducing agents such as V(II) are kinetically effective for the reductive dissolution of iron oxides such as Fe3O4, Fe2O3, etc. To develop a methodology for large-scale synthesis of V(II), we report here the details of an electrolytic preparation on a pilot-plant scale (50 L). It is demonstrated that, by using stainless steel mesh cathode and anode in a poly(tetrafluoroethylene)-lined stainless steel tank, V(II) could be prepared. To minimize the electrolysis duration for the conversion of V(V) to V(II), laboratory studies are carried out for a preliminary reduction of V(V) to V(IV) with hydrazine or ascorbic acid and then employing V(IV) for electrolysis. Here, the use of hydrazine was advantageous (30% less time) over that of ascorbic acid. The V(II) obtained was complexed with nitrilotriacetic acid (NTA), and its stability and dissolution kinetics of Fe2O3 and Fe1.6Cr04O3 in the VII-NTA formulation are reported.

Electrowinning and refining at the Williams Mine, using knitted stainless steel mesh cathodes

The Williams Mine mines and mills 6000 t/d (6600 stpd) of gold ore using SAG/ball milling, leaching and CIP, electrowinning and refining. Electrowinning, high-pressure cathode washing, filtering, retorting and refining are based around the use of knitted stainless steel mesh cathodes. Their primary advantage over conventional steel wool cathodes is that electrowon gold can be washed off, and the cathode can then be reused. Typically, the knitted cathodes have a useful life of up to 15 months. Gold production of up to 1.5 t/month (50,000 oz/month) is easily processed with this system. Presented is a description of this operation, including a review of the equipment and performance data.