Mining valuable minerals from seawater: A critical review

©2017 The Royal Society of Chemistry. Seawater contains large quantities of valuable minerals, some of which are very scarce and expensive in their land-based form. However, only a few minerals, the ones in high concentrations, are currently mined from the sea. Due to recent problems associated with land-based mining industries as a result of depletion of high-grade ores, sustainable water and energy demand and environmental issues, seawater mining is becoming an attractive option. This paper presents a comprehensive and critical review of the current methods of extracting valuable minerals from seawater and seawater brines generated in desalination plants, and suggests ways to overcome some of the limitations and challenges associated with the extraction process. The extraction methods discussed are solar evaporation, electrodialysis (ED), membrane distillation crystallisation (MDC), and adsorption/desorption

Comparison of membrane distillation and freeze crystallizer as alternatives for reverse osmosis concentrate treatment

© 2017 Elsevier B.V. Membrane distillation (MD) and freeze crystallizer (FC) were evaluated as alternative reverse osmosis concentrate (ROC) treatment options. A direct contact MD (DCMD) was capable of obtaining 60% water recovery with chemically pretreated ROC. Nevertheless, in repeated cycles, DCMD displayed a trend of reduced water recovery and declining permeate quality. At elevated concentrations, ROC caused scaling and membrane hydrophobicity reduction, indicating reduced membrane life span. On the other hand, FC in three-stage freeze/thaw approach was able to concentrate ROC by 2.3 time, achieving a 57% water recovery with no scaling issues. The fresh ice water quality (total dissolved solids) obtained from FC was within the range of 0.08–0.37 g/L. A brief techno-economic evaluation highlighted advantages and limitations of both options. The efficiency of DCMD as a compact, low thermal process for ROC treatment was compromised by membrane scaling, indicating the necessity for a scaling mitigation pretreatment. This invariably incurs an additional cost. FC was advantageous as a scaling and chemical free process. The high freezing requirement of FC could be met by coupling with refrigerant coolant from liquefied natural gas. Nevertheless, the practical industrial application of FC is inherently restricted due to complex scaling up issues

AERODYNAMIC PERFORMANCE ANALYSIS OF CO-FLOW JET AIRFOIL

The work in this paper aims to increase the maximum lift coefficient of the airfoil by implementing the co-flow jet concept on NACA 0018 airfoil and also to investigate the performance of co-flow jet (CFJ) airfoil. To conduct numerical solution, RANS equations have been solved for 2D incompressible and unsteady flow using the Spalart-Allmaras turbulence model. The suction surface of the airfoil is modified by placing the injection slot near the leading edge and the suction slot near the trailing edge. A small mass of air is withdrawn into the airfoil suction slot, pressurized by a pumping system located inside the airfoil, and re-injecting into the injection slot tangentially to the main stream flow. The CFJ airfoil is enhancing the aerodynamic lift coefficient significantly compare to the baseline airfoil. And also, the numerical analysis is carried out to investigate the effect of the location of injection and suction slot. And it is observed that the aerodynamic lift coefficient of CFJ airfoil is increasing with varying the injection slot away from the leading edge

The role of mirror neurons in movement suppression

The characteristic feature of mirror neurons is that they modulate their firing rate during both a monkey’s own action and during observation of another individual performing a similar action. Some premotor (F5) mirror neurons have also been shown to be corticospinal neurons, meaning that spinal targets are also influenced during action observation. Simultaneous electromyography (EMG) recordings from hand and arm muscles provide important evidence that the activity of these cells cannot be explained by any covert movement on the part of the monkey. The question arises as to how output cells (pyramidal tract neurons, PTNs) that are classically involved in the generation of movement can be modulated without any resulting movement. Since there are many more PTNs in primary motor cortex (M1) compared with F5, it is important to assess whether PTNs in M1 also have mirror activity. We recorded activity of identified PTNs in areas M1 and F5 of two macaque monkeys during action execution and observation of a skilled grasping action. We found evidence of modulation of PTNs in M1 during action observation in over half the recorded units. However, the depth of modulation was much smaller during action observation compared with action execution. In a separate analysis we investigated whether it is possible to assign mirror neuron activity to different cell types on the basis of extracellular spike duration. Surprisingly, we found considerable overlap between identified pyramidal cells and putative interneurons and provide evidence 4 that spike duration alone is not a reliable indicator of cell type in macaque motor cortex. In a separate series of studies we used non-invasive transcranial magnetic stimulation (TMS) in human volunteers to measure the corticospinal excitability during the same task. Taken together, although we found evidence of modulation of PTN activity during action observation in M1, the level of activity was greatly reduced during action observation and may not be sufficient to produce overt muscle activity

Selective copper extraction by multi-modified mesoporous silica material, SBA-15

© 2018 Selective copper (Cu) recovery from wastewater mitigates environmental pollution and is economically valuable. Mesoporous silica adsorbents, SBA-15, with amine-grafting (SBA-15-NH2) and manganese loading along with amine-grafting (Mn-SBA-15-NH2) were fabricated using KMnO4 and 3-aminopropyltriethoxysilane. The characteristics of the synthesized adsorbents were evaluated in detail in terms of its crystal structure peaks, surface area and pore size distribution, transmission electron microscope and X-ray photoelectron spectroscopy. The results established the 2.08 mmol/g of Cu adsorption capacity on Mn-SBA-15-NH2. Furthermore, in a mixed heavy metal solution, high selective Cu adsorption capacity on Mn-SBA-15-NH2 (2.01 mmol/g) was achieved while maintaining 96% adsorption amount as that of a single Cu solution. Comparatively, Cu adsorption on SBA-15-NH2 decreased by half due to high competition with other heavy metals. Optimal Cu adsorption occurred at pH 5. This pH condition enabled grafted amine group in Mn-SBA-15-NH2 to form strong chelating bonds with Cu, avoiding protonation of amine group (below pH 5) as well as precipitation (above pH 5). The adsorption equilibrium well fitted to Langmuir and Freundlich isotherm models, while kinetic results were represented by models of linear driving force approximation (LDFA) and pore diffusion model (PDM). High regeneration and reuse capacity of Mn-SBA-15-NH2 were well established by its capacity to maintain 90% adsorption capacity in a multiple adsorption-desorption cycle. Cu was selectively extracted from Mn-SBA-15-NH2 with an acid solution

Fractional-submerged membrane distillation crystallizer (F-SMDC) for treatment of high salinity solution

© 2018 Elsevier B.V. Membrane distillation with crystallization (MDC) is an attractive process for high saline seawater reverse osmosis (SWRO) brine treatment. MDC produces additional fresh water while simultaneously recovering valuable resources. This study developed a novel approach of fractional-submerged MDC (F-SMDC) process, in which MD and crystallizer are integrated in a feed tank with a submerged membrane. F-SMDC principle is based on the presence of temperature/concentration gradient (TG/CG) in the feed reactor. The operational conditions at the top portion of the feed reactor (higher temperature and lower feed concentration) was well suited for MD operation, while the bottom portion of the reactor (lower temperature and higher concentration) was favourable for crystal growth. F-SMDC performance with direct contact MD to treat brine and produce sodium sulfate (Na2SO4) crystals using TG/CG showed positive results. The TG/CG approach in F-SMDC enabled to achieve higher water recovery for brine treatment with a volume concentration factor (VCF) of over 3.5 compared to VCF of 2.9 with a conventional S-MDC set-up. Further, the high feed concentration and low temperature at the reactor bottom in F-SMDC enabled the formation of Na2SO4 crystals with narrow crystal size distribution

Rubidium recovery using potassium cobalt hexacyanoferrate sorbent

© 2016 Balaban Desalination Publications. All rights reserved. Rubidium (Rb) is a highly valued and economically important metal present in large quantities in many natural and wastewaters. However, its recovery is hampered by its low concentration and extracting agents’ limited selectivity. A batch sorption study showed that a potassium cobalt hexacyanoferrate (KCoFC) sorbent had much higher sorption capacities for Rb and caesium (Cs) than for lithium (Li), sodium (Na) and calcium (Ca). Equilibrium sorption data at pH 7 and 24 ± 1°C for Rb and Cs satisfactorily fitted to the Langmuir model with sorption maxima of 96 and 61 mg/g, respectively. A fixed-bed column (12 cm height) containing a mixture of 2.2 g KCoFC and 19.8 g granular activated carbon had a breakthrough sorption capacity of 61 mg/g when a solution containing 5 mg Rb/L was passed through the column at a velocity of 2.5 m/h (0.7 L/h). When 1 and 5 mg Cs/L were added to the Rb solution, Rb sorption capacity dropped to 46 and 41 mg/g, respectively. During Rb sorption, K from the KCoFC lattice was released. Leaching the column containing sorbed Rb with 0.1 M KCl for 60 min at a velocity of 10 m/h desorbed 99% of sorbed Rb. A process for recovering Rb from sea water reverse osmosis brine is presented

Effect of chemical and physical factors on the crystallization of calcium sulfate in seawater reverse osmosis brine

© 2017 Elsevier B.V. A major challenge of seawater reverse osmosis (SWRO) desalination process corresponds to the management of concentrated brine waste because discharging the brine back into the sea influences the marine ecosystem and incurs additional costs to plants. A membrane distillation crystallizer (MDC) can further produce clean water and simultaneously recover valuable resources from the concentrated brine; this is more environmentally and economically optimal. SWRO brine contains salts, which contribute to scaling development during the MDC operation. Hence, the main goals of this study was to observe the crystallization tendency of calcium sulfate (CaSO4) under high salinity and, to examine other inorganic and organic compounds and operational conditions that affect the CaSO4 crystallization. The crystallization tendency of CaSO4 in SWRO brine was examined with respect to different temperatures; changes in pH values; and in the presence of co-existing ions, chemical agents, and organic matters as well as physical factors. The results showed that the size and quantity of crystals formed increased at higher temperatures. Furthermore, an increase in the pH values increased the crystal size. At higher pH, the complexion of NaCl along with CaSO4 was created. Moreover, stirring enhanced CaSO4 crystal formation due to the kinetic mechanism