Bench-scale Tests Research Articles

High temperature permittivity measurements of selected industrially relevant ores: Review and analysis

The mineral processing and extractive metallurgy industries are under increasing pressure to develop more energy efficient and sustainable technologies. As a result, there is increasing interest in the application of alternative energy sources, such as microwave technology. While bench scale testing has been conducted in this area for over thirty years, scale-up has remained a key challenge. One barrier to implementation has been the lack of understanding of the fundamental interaction of microwaves with ores. Key parameters include the real and the imaginary permittivities, which influence both the heating rate and the microwave penetration depth. Over the last decade, high temperature permittivity measurements have been performed on various ores using the cavity perturbation technique. In this paper, this permittivity data is presented as a function of temperature primarily at 912 MHz. Based on the interpretation of this data, recommendations are made for the sustainable utilization of microwave technology in metallurgical processing.

One-step Ferrate(VI) treatment as a core process for alternative drinking water treatment.

Traditional water treatment plants adopt multiple treatments to sequentially treat raw water for producing potable water. Besides complex treatment design and operation, they typically require a large space to accommodate different reactors. Furthermore, emerging issues (e.g. poor removal of persistent micro-pollutants) challenge the conventional treatment train. In this study, bench-scale tests were performed with real surface waters to evaluate ferrate(VI) treatment as a key alternative process for traditional water treatment. Of note, most earlier investigations on ferrate(VI) for water treatment utilized ferrate(VI) merely for pre- or post-treatment or simply as a disinfecting agent. Fundamentally different from the previous efforts, this study aimed to assess whether one-step ferrate(VI) addition, coupled with sedimentation, provided a comprehensive treatment, better than or equivalent to conventional surface water treatment. Results show that ferrate(VI) could simultaneously and effectively remove turbidity, degrade natural organic matter (NOM), and inactivate bacterial indicators in one single dose. The treatment performance relied heavily on ferrate(VI) dose and pH. Generally, higher ferrate(VI) dose improved the treatment results, except that it might re-suspend particles at a high dose at an alkaline condition. Lower pH favored coagulation due to reduction of zeta potentials on particle surface and promotion of their aggregation and enhanced the degradation of NOM because of higher Fe(VI) reactivity toward reductive moieties. In contrast, higher pH benefited the disinfection efficiency due to better stability and greater exposure of ferrate(VI). This study demonstrates that ferrate(VI) treatment can serve as a core treatment process in alternative water treatment designs for addressing various challenges.

Combustion toxicity regulations for construction products

Research literature comparing room-scale combustion toxicity performance of construction products is compared to bench-scale results. It is demonstrated that it is inappropriate the regulate construction products on the basis of performance in bench-scale toxicity tests, while it is economically unsound to suggest requiring room-scale testing for assessing combustion toxicity hazards. Instead, it is demonstrated that the combustion toxicity hazards of construction products are best addressed by regulating their heat release rate characteristics.

Techno-economic analysis of producing liquid fuels from biomass via anaerobic digestion and thermochemical conversion

This paper discusses a preliminary design and a techno-economic analysis of a process that produces liquid hydrocarbon fuels from biomass through a combined biochemical and thermochemical process. The biochemical component involves anaerobic digestion (AD) of the biomass's biodegradable portion to produce biogas. Biogas is purified by removing contaminants and upgraded to liquid hydrocarbon fuel in a biogas to liquid facility (BGTL) via thermochemical conversion route. The BGTL process involves two major steps: tri-reforming to produce syngas (a mixture of CO and H2), and, Fischer-Tropsch Synthesis (FTS) to convert the syngas to a spectrum of hydrocarbons (synthetic crude). Separation and upgrading of the produced hydrocarbon mixture allows production of transportation fuels such as gasoline, jet fuel, and diesel.In order to evaluate the economics of the combined process a detailed process modelling was carried out using Aspen Plus® software. Bench-scale experimental results served as the basis of modelling the BGTL section of the plant, while the AD portion of the plant is based on empirical models selected from the literature validated by comparison with experimental results. Recent bench scale tests in our lab were used to determine processing parameters (yield, temperature, and pressure) for the reforming and FTS conversion.A plant capable of processing 90,000 tonne year−1 of wet biomass feed was designed and analyzed using the model. Results of the economic analysis estimate that a breakeven cost of diesel of $1.30 L-1 is achievable without the consideration of charging tipping fees to accept the biomass feedstock. Sensitivity study shows that the economics are significantly affected by the fixed capital investment (FCI) and less so by the operating expenses and interest rate. In addition, tipping fees and biomass feedstock cost have a substantial effect on the breakeven price of diesel.

Effect of temperature on chlorine treatment for elimination of freshwater phytoplankton in ballast water: bench-scale test

Chlorine efficacy as a biocide for ballast water treatment was investigated under cold- and warm-water temperatures across winter and summer seasons. Freshwater phytoplankton samples were collected and acclimated under in situ environmental conditions ranging from 2 to 22 °C. Samples were exposed to seven chlorine treatments (from 0.02 to 5.0 ppm), in addition to a control (0.0 ppm). Free-chlorine concentrations, phytoplankton abundance, and photosynthetic efficiency were measured up to 48 h following treatment. After 4 h of treatment at concentrations less than 0.22 ppm, phytoplankton densities were reduced by more than 50%, without cell resurgence. Similar reduction was recorded immediately after exposure when chlorine concentrations were higher than 3.0 ppm. After 8 h, free chlorine neared 0.0 ppm for initial chlorine concentrations below 1.2 ppm, irrespective of temperature regime. Winter phytoplankton exhibited slightly lower mortality to chlorine exposure regardless of the temperature, although they also exhibited lower photosynthetic efficiency. Despite a general absence of significant effect of temperature on the chlorine decay, our results suggest that higher doses of chlorine or longer exposure times may be required during winter to achieve full treatment effect. Tests at large scales are needed to further confirm these findings.

Bench-scale column evaluation of factors associated with changes in N-nitrosodimethylamine (NDMA) precursor concentrations during drinking water biofiltration

Biofiltration has been observed to increase or decrease the concentrations of N-nitrosodimethylamine (NDMA) precursors in the effluents of full-scale drinking water facilities, but these changes have been inconsistent over time. Bench-scale tests comparing biofiltration columns side-by-side exposed to different conditions were employed to characterize factors associated with changes in NDMA precursor concentrations, as measured by application of chloramines under uniform formation conditions (UFC). Side-by-side comparisons of biofiltration media from different facilities fed with water from each of these facilities demonstrated that differences in source water quality were far more important than any original differences in the microbial communities on the biofiltration media for determining whether NDMA precursor concentrations increased, decreased or remained constant across biofilters. Additional tests involving spiking of specific constituents hypothesized to promote increases in NDMA precursor concentrations demonstrated that inorganic nitrogen species associated with nitrification, including ammonia, hydroxylamine and chloramines, and biotransformation of known precursors (i.e., municipal wastewater and the cationic polymer, polyDADMAC) to more potent forms were not important. Biotransformation of uncharacterized components of source waters determined whether NDMA precursor concentrations increased or decreased across biofilters. These uncharacterized source water component concentrations varied temporally and across locations. Where biotransformation of source water precursors increased NDMA precursor concentrations, ∼30–60% of the levels observed in column effluents fed with biofiltration influent water remained associated with the media and could be rinsed therefrom in either the dissolved or particulate form. Ozone pre-treatment significantly reduced NDMA precursor concentrations at one facility, suggesting that pre-oxidation could be an effective technique to mitigate the increase in NDMA precursor concentrations during biofiltration. Biofiltration decreased the concentrations of halogenated disinfection byproduct precursors.

Selective flotation separation of molybdenite and chalcopyrite by thermal pretreatment under air atmosphere

The flotation separation of molybdenite and chalcopyrite is very difficultly due to their excellent natural floatability. Thermally pretreat minerals under 250 °C before flotation was investigated as a potential approach for the flotation separation of molybdenite and chalcopyrite. The bench-scale flotation tests of single mineral were carried out and showed that chalcopyrite lost its floatability in flotation process. Whereas for molybdenite, it maintained good floatability.Based on the thermal pretreatment method, the flotation separation of molybdenite and chalcopyrite was realized for both mixed binary minerals and Cu-Mo bulk concentrates without addition of depressant. The XPS analysis results showed that the oxidation degree of chalcopyrite was much higher than that of molybdenite. For chalcopyrite, the oxidation products were hydrophilic species, which made it cannot be recovered in the flotation process. For molybdenite, despite slight surface oxidation, the little changes of surface S species made it still can be easily recovered in the flotation process. According to these findings, the thermal treatment method can be potentially applied as an effective route to separate Cu-Mo sulfide ore.

Runout estimates and risk-informed decision making for bench scale open pit slope failures

Bench scale open pit slope failures are common occurrences in open pit mines and present a hazard to workers near freshly excavated faces. Objectively forecasting the zone of influence of bench scale failures is an important component of the mine’s risk management plan, as they occur more frequently than multi-bench scale landslides and can be more difficult to monitor. This paper presents a dataset of 167 bench scale open pit slope failures and tests runout and bench-width sizing methods to identify appropriate tools to estimate a stand-off distance from a fresh bench face. A length versus fall height and a Fahrböschung angle versus volume relationship calibrated to bench scale open pit slope failures provide reasonable runout estimates and are useful for decision-making when workers are near freshly excavated bench faces. Bench scale open pit failures appear to have a relatively constant fall height/horizontal runout distance (H/L) ratio up to 10 000 m3, after which H/L becomes inversely proportional to volume.

Nanomaterial Adsorbent Design: From Bench Scale Tests to Engineering Design.

Nanomaterial Adsorbent Design: From Bench Scale Tests to Engineering Design.

Effect of pre-coagulation using different aluminium species on crystallization of cake layer and membrane fouling

Pre-coagulation could mitigate the membrane fouling, and thus we used different Al coagulants as a pre-treatment for ultrafiltration to explore their effects on the morphology of the membrane cake layer and fouling. Parallel bench-scale tests, using three different species of Al (AlCl3, PACl15, and PACl25), with and without humic acid, were operated continuously for a long period to investigate the effects of floc aging (~13 days). Specifically, the presence of humic acid affects the cake layer by influencing the rate and extent of floc crystallization, as greater crystallization leads to greater fouling (bio-fouling was excluded in this study). The fouling rate (indicated by the trans-membrane pressure at constant flux) varied with Al species and was found to increase as follows: PACl15 < PACl25 < AlCl3. The presence of humic acid also intensify membrane flouling. The results showed that three species of Al induced different sizes of primary nanoparticles and fractal dimensions of flocs, and therefore produced cake layers with different thickness/structure. Analysis of flocs with different ages indicated a crystallization process in the cake layer. Crystallization exacerbate membrane fouling by decreasing the porosity of the cake layer, and the situation became severe in the presence of humic acid.

Isolation and characterization of novel bacterial strains for integrated solar-bioelectrokinetic of soil contaminated with heavy petroleum hydrocarbons

This study investigated the isolation and characterization of three novel bacterial strains; Acinetobacter calcoaceticus, Sphingobacterium multivorum, and Sinorhizobium, isolated form agriculture land. From three hundred strains of bacteria, the three isolates were identified for their superior diesel degradation ability by a series of bench-scale tests. The isolates were further investigated in bench tests for their ability to grow in different diesel fuel concentrations, temperature and pH; degrade diesel fuel in vitro; and for the identification of functional genes. Semi-pilot bioelectrokinetic tests were conducted in three electrokinetic cells. An innovative electrode configuration was adopted to stabilize the soil pH and water content during the test. The genes expressed in the diesel degradation process including Lipases enzymes Lip A, LipB, Alk-b2, rubA, P450, and 1698/2041 were detected in the three isolates. The results showed that the solar panel voltage output is in agreement with the trapezoid model. The temperatures in the cells were found to be 5–7 °C higher than the ambient temperature. The electrode configuration succeeded in stabilizing the soil pH and water content, preventing the development of a pH gradient, important progress for the survival of bacteria. The diesel degradation in the soil after bioelectrokinetic tests were 20–30%, compared to 10–12% in the controls. The study succeeded in developing environmentally friendly technology employing novel bacterial strains to degrade diesel fuel and utilizing solar panels to produce renewable energy for bioelectrokinetics during the winter season.

Tecnologias avançadas de tratamento visando à remoção de cor e fenol de efluente de indústria de celulose e papel

Na produção de celulose e de papel são utilizados elevados volumes de água, madeira e ampla variedade de produtos químicos, gerando efluentes com características diversas em termos quantitativos e qualitativos, a depender do processo produtivo empregado. Trata-se de um efluente parcialmente biodegradável, entretanto, parte considerável dos componentes presentes nesses efluentes são dificilmente removidos em processos biológicos convencionais de tratamento de águas residuárias. Assim, estudar formas de melhoria da qualidade final desses efluentes, a partir de tecnologias mais avançadas de tratamento, vai de encontro à inovação tão almejada por esse setor altamente competitivo e globalizado, que é o mercado da celulose e papel. O presente artigo teve como enfoque a remoção de cor e fenol a partir do emprego da coagulação/floculação/sedimentação empregando tanino vegetal como agente coagulante, em detrimento ao uso de coagulantes sintéticos convencionais e filtração em carvão ativado granular (CAG). Os principais resultados obtidos foram remoções de: 89% da cor e 60% do fenol no tratamento por coagulação, floculação e sedimentação; 45% da cor e 47% do fenol no tratamento por filtração em carvão ativado e 99% da cor e acima de 93% de fenol ao tratar o efluente por ciclo completo (coagulação, floculação, sedimentação seguido de filtração). Com esse último tratamento foi possível obter efluente final com elevada qualidade e atender à legislação ambiental sob diversos aspectos.

Enhancing methane production of anaerobic sludge digestion by microaeration: Enzyme activity stimulation, semi-continuous reactor validation and microbial community analysis

Effects of microaeration pretreatment on sludge hydrolysis, biogas production and microbial community structure in anaerobic digestion (AD) were investigated by bench-scale tests and semi-continuous experiments. Bench tests showed that microaeration led to the release of dissolved organic matters, generation of volatile fatty acids and stimulation of enzyme activity. Correlation analysis showed that methane production was significantly correlated with the activity of α-glucosidase at 0.01 level, and with protease activity, released polysaccharides and VFAs at 0.05 level. Semi-continuous experiments showed that microaeration accelerated the utilization of organic matters, increased biogas production by 16.4%, enhanced methane content in biogas, and improved sludge dewaterability. Microbial community structure analysis showed that microaeration promoted enrichment of hydrolytic and fermentative bacteria in AD reactor rather than methanogenic bacteria, and aceticlastic methanogenesis was the main methanogenic pathway for methane production.

Verification of proper operation of dry acid gas removal process on syngas derived by O2/CO2-blown gasifier

Dry syngas purification process was demonstrated on the bench scale test facility comprised of halide removal unit and sulfur removal unit with three fixed bed reactors in which regenerable honeycomb sorbents were installed. The first-ever test of the facility aims to verify the resistance of the zinc ferrite desulfurization sorbent to the carbon deposition in actual syngas condition and proper operation of the cyclic run of the three-reactors system. The test was so challenging that the sulfur removal sorbent was exposed to the severe condition for carbon deposition in the actual syngas derived from oxygen/carbon dioxide blown coal gasifier. The process was operated at 450 °C and 0.98 MPa abs. under the duration of reactor switching of sulfur removal unit of 1 hr for the initial cyclic operation. The dry syngas purification process exhibited sufficient performance of halide and sulfur removal that was evaluated with gas analytical instruments and chemical analysis of the spent sorbent. The sulfur removal unit was operated for the initial cycle of sulfidation, regeneration, and reduction steps without any detrimental effect of carbon deposition. This result encouraged that the process is ready to perform the proper operation in the actual syngas condition during the longer duration of multiple cyclic operation of the bench scale test facility.

In-service performance of hybrid geopolymer binders based class F fly ash

Production of high-performance construction materials, meeting the requirements of construction process when development of up-to-date buildings and structures is very relevant and requires the usage of effective polycomponent binding systems, including geopolymers This work studied mechanical performance, as well as strength, water absorption and water resistance of portland cement – Class F fly ash – NaOH hybrid geopolymer binding system. The bench scale testing was conducted on different mixes, including regular portland cement-based and Class F fly ash-NaOH geopolymer binders used as reference compositions. The developed hybrid binders demonstrated, that incorporation of portland cement up to 40% as a modifying agent, reduces the formation of water soluble mineral phases such as sodium carbonates and hydroxycarbonates in low reactive class F fly ash geopolymer binders. It was found, that the presence of portland cement in the system positively affects strength development and noticeably reduces water absorption and improves water resistance of the developed binders, which is related to formation of water resistant and stable calcium hydrosilicate phases (C-S-H)

Remediation of heavy-metal-contaminated sediments in USA using ultrasound and ozone nanobubbles

The lower 12·875 km of the Passaic River (NJ, USA) is heavily contaminated due to industrial activities – specifically heavy metal extraction from chromium (Cr)-ore-processing plants and production of pesticides and herbicides. Conventional methods for remediating contaminated sediments have limited application due to the tidal action and urban development of the contaminated section of the Passaic River. Hence, this study proposes an in situ technology using ultrasound and ozone (O3) nanobubbles to remediate the sediments. Ultrasound is capable of desorbing heavy metals from soil, and ozone can oxidise the released heavy metals to a form that is mobile for ease of extraction. Nanobubbles are used as an effective ozone delivery method for the oxidation of heavy metals. Bench-scale tests were performed to evaluate the feasibility of the proposed technology. Ozone nanobubbles increased the solubility of ozone in water and reduced wastage. Also, due to the high ozone concentrations in water, chromium oxidation increased. A synthetic soil with a grain size distribution similar to that of actual river sediments was artificially contaminated with chromium and used in this research. Test results showed a 97·54% chromium removal efficiency, suggesting the feasibility of the proposed technology for pilot-scale studies.

A Multi-Scale Analysis of the Fire Problems in an Urban Utility Tunnel

Building utility tunnels has been widely adopted as an important solution for the sustainable development of cities, but their unique fire problems have not attracted enough attention to date. With the purpose of preliminarily understanding the fire phenomena in a utility tunnel, this study performed a comprehensive analysis, including the burning behaviour of accommodated cables, hot gas temperature field and enhanced fuel burning rates based on bench-scale, full-scale and model-scale fire tests. The critical exposed radiative heat flux for the 10-kV power cable to achieve complete burning was identified. The whole burning process was divided into five phases. The cable’s noteworthy hazards and dangerous fire behaviours were also examined. The two-dimensional (2D) gas temperature fields and longitudinal maximum temperature distributions were investigated carefully, after which a versatile model was derived. The model predicted the maximum temperature attenuation of both upstream and downstream flows reasonably well. Finally, the phenomenon of enhanced fuel burning was explored. A multivariate cubic function that considers the global effects of relative width, height and distance was further proposed to estimate the enhancement coefficient. The current findings can provide designers and operators with valuable guidance for the integrated promotion of utility tunnels’ fire safety level.

Large-Scale and Bench-Scale Test Systems for Assessing Impact of Geogrids on Pavements Founded on Problematic Soils

Abstract Geogrid reinforcement is an economically viable alternative to achieve improved performance in highway pavement construction in regions with soft problematic subgrade soils. To examine the potential benefits of using geogrids in pavement foundations, measurement of permanent deformation using laboratory triaxial tests is typical practice. However, since the performance improvement of pavement foundation systems is achieved by distribution of vertical stresses at the reinforcing layer through the tensile properties of the geogrid material, it is desirable to conduct large-scale testing to more accurately monitor the behavior of the geogrid-reinforced aggregate and soil system. This article describes the development of laboratory large-scale and bench-scale pavement testing systems to evaluate the behavior of geogrid-reinforced pavement systems through wheel tests performed with problematic subgrade soils found in North Georgia. The large-scale test specimens are prepared in a 1.8 (6 ft) by 1.8 (6 ft) by 0.6 m (2 ft) metal box and consist of 305 mm (12 in.) of unbound aggregate base (UAB) overlying 305 mm (12 in.) of subgrade soil. Geogrid is placed at the interface between the subgrade soil and UAB layer. Pressure sensors are installed near the bottom of the UAB layer and near the top and bottom of the subgrade layer to monitor stress distributions within the pavement foundation system. The bench-scale system, which measures 914 (36 in.) by 203 (8 in.) by 152 mm (6 in.) is also described. This system is advantageous because not only does it expedite rapid testing but also allows for relative micro- and macroscale comparisons of aggregate-geogrid behavior. This article presents test results showing vertical stress variations obtained experimentally in the UAB and subgrade soils under simulated traffic tire loading. The two systems are shown to be effective in establishing the influence of geogrid reinforcement in pavement systems.

Analysis of heavy metals fixation and associated energy consumption during sewage sludge combustion: Bench scale and pilot test

The combustion is an effective way of sewage sludge treatment and provides an attractive source of energy. However, the heavy metals (HMs) volatilization and the energy demand are restrictive factors for sewage sludge combustion. This study focused on the heavy metals fixation with the sorbents addition and the energy balance of sludge combustion using the bench scale and pilot tests. The proximate and the combustion characteristic analysis showed that the volatile component burning played a dominant role during the combustion of the sludge, but the reaction mechanisms for their combustion steps were different. Bench-scale tests indicated that with 6.25% kaolin addition, temperature of 900 °C, and residence time of 20 min, the fixation ratios of Cu, Pb, Ni, Cd, Cr, and Zn were reached 94.60%, 90.69%, 93.75%, 90.71%, 92.21%, and 96.53%, respectively. Long-term pilot tests demonstrated that the energy consumption for the combustion of one ton dehydrated sludge could be as low as 62 kW h with a 10-m long electric heating rotary kiln. Furthermore, the escaped Pb, Cd, Cr, Cu, Ni, and Mn were only 2.12 g, 0.12 g, 0.86 g, 33.90 g, 1.61 g, and 66.67 g, respectively, per ton dried sludge. This study can provide an environmentally friendly and economical way of treating sludge.

The selective flotation behavior and adsorption mechanism of thiohexanamide to chalcopyrite

In this paper, thiohexanamide (THA) surfactant was synthesized and introduced as a collector for sulphide ores. The flotation behavior of THA to sulphide ores was investigated by micro-flotation tests, bench-scale tests and adsorption quantity measurements. The results demonstrated that compared to O-isopropyl-N-ethyl-thionocarbamate (IPETC), THA exhibited superior selectivity to chalcopyrite against pyrite and galena. In comparison with another chalcopyrite collector sodium isobutyl xanthate (SIBX), THA showed stronger flotation affinity to chalcopyrite. UV/vis spectra results illustrated that THA can selectively reacted with Cu+ than with Fe2+ or Pb2+. The adsorption mechanism of THA to chalcopyrite was evaluated by FTIR spectra, zeta potential measurements and XPS analysis. The conclusion was further confirmed by density functional theory (DFT) calculations. Two adsorption geometries were suggested, one with the formation of a four-membered ring complex, another with the connection between just Cu and S atoms.