Acidic Mine Waters (AMWs) are characterised by high acidity (pH < 3) as H2SO4 and elevated contents of metals (Al, Fe, Cu, Zn), including rare earth elements (REEs). Due to the exhaustion of minable ...REE containing-minerals, AMWs are increasingly regarded as an alternative source of REEs. Among the different alternatives for the pre-concentration of AMWs required to make the REE extraction possible, nanofiltration (NF) membranes emerge as a promising technology because they not only successfully reject multivalent ions (metals), allowing its concentration in the retentate stream, but also permit the transport of monovalent ones, such as H+ and HSO4−, allowing the recovery of sulphuric acid in the permeate. Despite this potential of NF, there is still a lack of modelling tools for predicting the performance of NF membranes because of its dependence on solution composition, membrane properties and interaction between both. In this study, a prediction tool based on the Solution-Electro-Diffusion model (including the effect of solution composition) was developed and experimentally validated for the application of two polyamide-based NF membranes (NF270 and Desal DL) for the recovery of REEs and H2SO4 from three different synthetic solutions mimicking AMWs (pH 1.0, 60 mg/L REEs and, 25–600 mg/L Al, Cu, Ca and Zn) differing in their Fe concentration (0–2125 mg/L). Metals were effectively rejected (>98%), whereas H2SO4 was transported across the membrane (H+ rejections <30%). The mathematical model was able to predict the performance of both membranes as well as the potential scaling events associated with Fe and Al hydroxides and hydroxy-sulphates.
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•Acidic mine waters as a potential source for chemicals recovery•Nanofiltration membranes for acid recovery and metal concentration•A numerical algorithm as a design tool for NF based separation processes•Use of Solution–Electro–Diffusion model to predict nanofiltration performance•Dependence of membrane permeances to species on solution composition
•Mg/Al LDH was employed for phosphate adsorption.•A maximum adsorption capacity of 71.2mg-P/L was obtained in 4h.•The phosphate uptake by Mg/Al LDH was in agreement with Freundlich model.•The ...adsorption was pH-dependent and was affected by competitive anions.•Phosphate adsorbed on LDH is effectively desorbed at acid and basic pH values.
In the present study, the adsorptive properties of phosphate on Mg/Al layered double hydroxides (LDHs) from aqueous solution were evaluated. The FTIR results confirmed the anionic exchange of the nitrate anions from the interlayer space with phosphate anions took place successfully. The kinetics experiments indicated that the kinetic models which best describe phosphate adsorption on LDHs are the pseudo-second order and intraparticle diffusion models. The effects of the pH and the amount of adsorbent on phosphate uptake were investigated and it was determined that the optimum conditions are pH 3 and 0.6g/L LDH. The equilibrium isotherms showed that the phosphate uptake by Mg/Al LDH was in agreement with Freundlich model with constants of logKF=1.84 and 1/n=0.52. The effect of interfering anions on the adsorption capacity was also evaluated in the presence of several competitive anions. The results showed that in presence of other ions phosphate ion uptake decreases in the order NO3−>HCO3−>Cl−>SO42−. The desorption studies showed that the phosphate adsorbed on LDH is effectively desorbed at acid and basic pH values.
The integration of up-concentration processes to increase the efficiency of primary sedimentation, as a solution to achieve energy neutral wastewater treatment plants, requires further post-treatment ...due to the missing ammonium removal stage. This study evaluated the use of zeolites as a post-treatment step, an alternative to the biological removal process. A natural granular clinoptilolite zeolite was evaluated as a sorbent media to remove low levels (up to 100mg-N/L) of ammonium from treated wastewater using batch and fixed bed columns. After being activated to the Na-form (Z-Na), the granular zeolite shown an ammonium exchange capacity of 29±0.8mgN-NH4+/g in single ammonium solutions and 23±0.8mgN-NH4+/g in treated wastewater simulating up-concentration effluent at pH=8. The equilibrium removal data were well described by the Langmuir isotherm. The ammonium adsorption into zeolites is a very fast process when compared with polymeric materials (zeolite particle diffusion coefficient around 3×10−12m2/s). Column experiments with solutions containing 100mgN-NH4+/L provide effective sorption and elution rates with concentration factors between 20 and 30 in consecutive operation cycles. The loaded zeolite was regenerated using 2g NaOH/L solution and the rich ammonium/ammonia concentrates 2–3g/L in NaOH were used in a liquid-liquid membrane contactor system in a closed-loop configuration with nitric and phosphoric acid as stripping solutions. The ammonia recovery ratio exceeded 98%. Ammonia nitrate and di-ammonium phosphate concentrated solutions reached up to 2–5% wt. of N.
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•A natural zeolite was evaluated to recover ammonium in column experiments.•Loaded zeolite was regenerated and rich concentrates were used in a LLMC system.•Hollow fibre liquid-liquid membrane contactors were used to produce liquid fertilizers.•The closed-loop configuration allowed recovery ratios of ammonia higher that 98%.•Concentrated solutions reached up to 2–5% wt. of N.
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•AMWs disposal is limited due to arsenic and selenium environmental regulations.•NF is proposed as a sustainable alternatively for traditional AMWs treatments.•Chemical precipitation ...was conducted before NF for Fe and As oxidation and removal.•REEs recovery, hazardous species removal and flow reduction was achieved by NF.•As & Se concentration was reduced below discharge limits by the proposed treatment.
Arsenic and selenium presence in acid mine waters (AMWs) limits their disposal due to environmental regulations. The focus to solve the economic infeasibility is directed to sustainable solutions, promoting resource recovery. In fact, rare earth elements (REEs) recovery is proposed in most of the Iberian Pyrite Belt AMWs. However, the presence of arsenic and selenium may impact in the REEs recovery. Among different alternatives, nanofiltration (NF) provides a concentration stage on REEs recovery, reduces the nominal flow and removes hazardous species. In this work, Iberian Pyrite Belt AMWs with up to 10 mg/L REEs, containing arsenic (2 mg/L), were treated with a NF membrane. Firstly, AMWs were pre-treated with H2O2/NaOH, to oxidise Fe(II) to Fe(II) and As(III) to As(V), promoting their removal and avoiding their potential precipitation at the membrane. Subsequently, NF pressure effect (6–20 bar) was studied, removing metals (>95 %), whereas arsenic rejections ranged from 60 to 71 %. Then, water recovery potential was evaluated at 10, 15 and 22 bar by reproducing a 10-stages NF plant. Results showed that the proposed treatment could be an alternative for arsenic and selenium removal (70 μg/L and 0.5 μg/L permeate concentrations, respectively) to achieve mining discharge limits according to regulations.
The global demand for valuable metals and minerals necessitates the exploration of alternative, sustainable approaches to mineral recovery. Seawater mining has emerged as a promising option, offering ...a vast reserve of minerals and an environmentally friendly alternative to land-based mining. Among the various techniques, Nanofiltration (NF) has gained significant attention as a preliminary treatment step in Minimum Liquid Discharge (MLD) and Zero Liquid Discharge (ZLD) schemes. This study focused on the potential of two underexplored commercial polyamide based NF membranes, Synder NFX and Vontron VNF1, with enhanced divalent over monovalent separation factors, in optimizing the extraction of magnesium hydroxide (Mg(OH)2) from seawater and seawater reverse osmosis (SWRO) brines. The research encompassed a thorough characterization of the membranes utilizing advanced physic-chemical analytical techniques, followed by rigorous experimental assessments using synthetic seawater and SWRO brine in concentration configuration. The findings highlighted the superior selectivity of NFX for magnesium recovery from SWRO brine and the promising concentration factors of VNF1 for seawater treatment. Cross-validation of experimental data with a mathematical model demonstrated the model's reliability as a process design tool in predicting membrane performance. A comprehensive techno-economic evaluation demonstrates the potential of NFX, operating optimally at 23 bar pressure and 70% permeate recovery rate, to yield an estimated annual revenue of 5.683 M€/yr through Mg(OH)2 production from SWRO brine for a plant with a nominal capacity of 0.8 Mm3/y. This research shed light on the promising role of NF membranes in enhancing mineral recovery taking benefit of their separation factors and emphasizes the economic viability of leveraging NF technology for maximizing magnesium recovery from seawater and SWRO brines.
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•NFX and VNF1 membranes were tested for seawater/brine valorization.•Tests were conducted at 20 bar and permeate recovery p.r (0–80%).•NFX showed higher Mg selectivity than VNF1 in both scenarios.•Mg(OH)2 purity >97% was reached (NFX, SWRO brine, 10 bar and p.r 80%).•The highest achieved revenue was 5.7 M€/yr (NFX, SWRO brine, 23 bar, p.r 70%).
•Compare different adding porous materials effect on solar pond temperature.•Two styles of outdoor salt gradient solar ponds were used to experimental study.•One dimensional model was used to ...estimate the solar pond temperature development.•Coal cinder shows better performance than other involved bottom treatments.•Adding coal cinder on bottom can obviously increase solar pond temperature.
A higher Low Convective Zone (LCZ) temperature is important for the Salt Gradient Solar Pond (SGSP) thermal engineering application, which is bound to bring a more extensive application. For this purpose, we studied on adding a layer of coal cinder at bottom of LCZ of solar pond, here coal cinder is the burning residues of coal. Temperature development of adding coal cinder at bottom of SGSP has been experimentally and theoretically studied. One dimensional transient numerical model was used to estimate the temperature development in SGSP. The outdoor experiments were used to qualitatively study the temperature evolution of different bottom treatments and porous materials influence, and also used to validate the mathematics model present in this paper. The results show that adding coal cinder at bottom of SGSP leads to a higher LCZ temperature than the traditional bottom treatment. Good consistency has been achieved in the simulation results and the experimental results. Finally, in order to estimate the effect of coal cinder used in large-scale solar pond, a numerical simulation was given and compared to the similar research. The results of this paper show that it can obviously increase LCZ temperature by adding coal cinder at bottom of LCZ, and as a cheap material with perfect thermal performance, it is suitable to be applied in practical SGSP.
Water scarcity in the Mediterranean basin has been solved by using seawater desalination reverse osmosis technology (SWD-RO). This technology produces brine which is discharged back into the sea ...resulting in an environmental impact on marine ecosystems. Under the circular economy approach, the aim of this work is to recover resources from NaCl-rich brine (~60–70g/L), e.g. in the form of NaOH and HCl, by integration of two ion exchange-based membrane technologies and quantify the electrical energy consumption. Electrodialysis (ED) incorporating monovalent selective cation exchange membranes as divalent ions purification and concentration of the NaCl present in the SWD-RO brine, was integrated with bipolar membrane ED (EDBM) to produce NaOH and HCl. Current densities of 0.30–0.40kA/m2 at two temperature ranges simulating different seawater temperature regimes (15–18°C and 22–28°C) were tested and a pure NaCl solution was used as starting concentrate stream. NaCl-rich brines with 100 or 200g NaCl/L were obtained by ED and then introduced in the EDBM stack producing HCl and NaOH up to 2M, depending on the initial concentrations. A minimum energy consumption of 1.7kWh/kg NaOH was calculated when working by EDBM with initial concentrations of 104g NaCl/L and 0.24M HCl and NaOH.
•Seawater desalination reverses osmosis (SWD-RO) brine was valorized as NaOH and HCl.•ED was used to purify and concentrate SWD-RO brine into divalent-free NaCl solutions.•100 to 200g NaCl/L brines were achieved by ED depending on current and temperature.•EDBM was applied to produce HCl and NaOH as chemicals for pH adjustment treatments.•NaOH and HCl up to 2M were obtained at 9V by EDBM using an ED pretreated brine.
Winery and olive mill industries generate large amounts of wastes causing important environmental problems. The main aim of this work is the evaluation of different membrane separation processes like ...microfiltration, ultrafiltration, nanofiltration, and reverse osmosis for the recovery of polyphenols from winery and olive mill wastes in aqueous solutions. Membrane processes were tested separately in a closed-loop system, and by an integration in a concentration mode sequential design (open-loop). Feed flow rate was varied from 1 to 10 mL min−1, and permeate samples were taken in order to measure the polyphenols concentration. The separation and concentration efficiency were evaluated in terms of total polyphenol content, and by polyphenols families (hydroxybenzoic acids (HB), hydroxycinnamic acids (HC), and flavonoids (F)), using high performance liquid chromatography. Results showed that MF and UF membranes removed suspended solids and colloids from the extracts. NF was useful for polyphenols separation (HB rejections were lower than for HC and F: HB rejections of 50 and 63% for lees filters and olive pomace extracts, respectively), and RO membranes were able to concentrate polyphenols streams (86 and 95% rejection from lees filters and olive pomace, respectively). Membranes sequential designs for lees filters and olive pomace extracts, using a selective membrane train composed by UF, NF and RO membranes, were able to obtain polyphenol rich streams and high-quality water streams for reuse purposes.
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•For MF and UF processes trans-membrane flux was dependent of the feed flow rate.•Trans-membrane flux was independent of the feed flow rate for NF and RO processes.•MF membranes (0.22–0.45 μm) removed impurities and suspended solids from samples.•UF membrane (30 kDa) rejected about 72% of flavonoids from lees filters extracts.•NF membranes (DURACID and NF270) were the most selective for polyphenols separation.
Fluorescence excitation emission matrix (FEEM) spectroscopy was used to evaluate its applicability as a tool to track dissolved organic matter (DOM) in a drinking water treatment plant (DWTP) that ...incorporates a conventional line (consisting in ozonation and GAC filtration) and a membrane-based line (consisting in ultrafiltration, reverse osmosis and mineralization) working in parallel. Seven sampling points within the different process stages were characterized monthly during 2014. A global Parallel Factor Analysis (PARAFAC) was used to pull out underlying organic fractions from the fluorescence spectra. Accordingly a five components model was selected to describe the system and the pros and cons of the model were discussed by analysis of the residuals. Among the five fluorescent components, those associated to humic-like matter (C1, C3 and C4) showed a similar season variability in the river water feeding the DWTP (which resembled that of UV254 and TOC), whereas the two components associated to protein-like matter (C2 and C5) exhibited a different behavior. The maximum fluorescence intensity values (Fmax) were used to quantify DOM removals across the plant. Compared to the conventional line, water from the UF/RO membrane-based line showed between 6 and 14 times lower fluorescence intensity signal for the humic-like components and between 1 and 3 for the protein-like components as compared to the conventional line. The differences in DOM composition due to seasonal variations and along the treatment trains point out the suitability of using fluorescence measurements over other parameters such as UV254 as a monitoring tool to help optimize operation conditions of each treatment stage and improve produced water quality in a DWTP.
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•Water quality from a Drinking Water Treatment Plant was characterized using FEEM-PARAFAC.•The time-lapse measurements identified two different trends in organic intake.•The position-lapse measurements showed selectivity in removing the organic fractions.•The performance of a full-scale membrane-line and a conventional-line were compared.
Theoretical models predict that the relative importance of facilitation and competition may vary inversely across gradients of abiotic stress. However, these predictions have not been thoroughly ...tested in the field, especially in semi-arid environments. In this study, we evaluated how the net effect of the tussock grass Stipa tenacissima on the shrub Pistacia lentiscus varied across a gradient of abiotic stress in semi-arid Mediterranean steppes. We fitted the relationship between accumulated rainfall and the relative neighbour index (our measures of abiotic stress and of the net effect of S. tenacissima on P. lentiscus, respectively), which varied across this gradient, to a quadratic model. Competitive interactions dominated at both extremes of the gradient. Our results do not support established theory. Instead, they suggest that a shift from facilitation to competition under high abiotic stress conditions is likely to occur when the levels of the most limiting resource are so low that the benefits provided by the facilitator cannot overcome its own resource uptake.
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