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The successful adoption and widespread implementation of innovative acid mine drainage treatment and resource recovery methods hinge on their capacity to demonstrate enhanced performance, economic viability, and environmental sustainability compared to conventional approaches. Here, an evaluation of the efficacy of chromium-based metal-organic frameworks and amine-grafted SBA15 materials in adsorbing europium (Eu) from actual mining wastewater was conducted. The adsorbents underwent comprehensive characterization and examination for their affinity for Eu. Cr-MIL-PMIDA and SBA15-NH-PMIDA had a highest Langmuir adsorption capacity of 69 mg/g and 86 mg/g, respectively, for an optimum level of pH 4.8. Preferential adsorption tests followed using real AMD collected at a disused mine in the north of Norway. A comparative study utilizing pH-adjusted real AMD revealed that Cr-MIL-PMIDA (88%) exhibited slightly higher selectivity towards Eu compared to SBA15-NH-PMIDA (81%) in real mining wastewater. While Cr-MIL-PMIDA displays excellent properties for the selective recovery of REEs, practical challenges related to production costs and potential susceptibility to chromium leaching make it less appealing for widespread applications. A cost-benefit analysis was then undertaken to quantify the advantages of employing SBA15-NH-PMIDA material. The study disclosed that 193.2 g of EuCl3 with 99% purity can be recovered by treating 1000 m3 of AMD.

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Due to increasing application in the green energy sector, rare earth elements (REEs) have become a precious commodity in the international market. The REEs, Yttrium (Y) and Lutetium (Lu) are used as catalysts in wide array of industries. SBA-15 modified with 1,4-phthaloyl diamido-propyltriethoxysilane (1,4-PA-APTES) ligands; and chromium based metal organic frameworks (MOF) modified with PMIDA (MIL-101-PMIDA) were prepared in this study as potential adsorbents for recovery of these elements. The adsorption capacities for Lu and Y on virgin SBA-15 were negligible. After modification of SBA-15, the Langmuir adsorption capacities for Lu and Y significantly increased to 17.0 and 17.9 mg/L, respectively. The Langmuir adsorption capacities of Lu and Y on PMIDA modified MIL-101 (MIL-101-PMIDA) were 63.4 and 25.3 mg/g, respectively. Higher adsorption capacities of the MOF are due to its higher surface area (1050 m2/g) and beneficial functional groups such as phosphonic group present on the adsorbent surface and it attributes to rapider REE adsorption on MIL-101-PMIDA than on1,4-PA-SBA. Lu adsorption capacity was 2.5 times higher than Y due to its superior ion-exchange capability with grafted phosphonic groups. Both adsorbents retained over 90% of adsorption capacity after 5 adsorption/desorption cycles which demonstrate the high structural stability of the materials.

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Continuous and selective recovery of copper (Cu) from heavy metal wastewater not only mitigates the pollution of environment but also can be applied for industrial field. Due to several advantages such as large pore size, easy modification, physical and chemical stabilities, mesoporous silica material, SBA-15, has been synthesized via hydrothermal reaction in this study. For enhancing the adsorption capacity and selectivity for Cu ions, prepared SBA-15 was modified with manganese loading and amine-grafting (MN-SBA) then granulated by alginic-acid (GMN-SBA), successfully. Adsorption capacities for heavy metals such as Cu, Zn, Ni and Mn were 2.11, 1.24, 1.74 and 1.25 mmol/g on MN-SBA and decreased to 1.23, 0.68, 0.86 and 0.65 when it was granulated. Even though the adsorption capacities of GMN-SBA for heavy metals decreased by 40-50%, it enabled easy regeneration and separation process when applied for continuous fixed-bed column adsorption mode. Specifically, the results demonstrated that GMN-SBA was able to be reused for 5 times while maintaining over 80% adsorption capacities. Fixed-bed adsorption results were well explained by dynamic adsorption model incorporated with linear driving force approximation (LDFA) model. The simulation of fixed-bed adsorption tests was proceeded in terms of bed length, feeding concentration and flow rate, and it showed the breakthrough times were shifted in the axis of time. In multi-component adsorption, LDFA model showed a high overshoot phenomenon of the breakthrough curves for Zn, Ni and Mn compared to Cu. This reflected the high affinity of Cu towards GMN-SBA compared to other heavy metals.

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Acid mine drainage (AMD) which involves high sulfur and heavy metals concentrations and furthermore are acidic in character, has been a major environmental and economic issue due to the associated toxicity and treatment costs. A large quantity of AMD in nature has a variety of resources including water and heavy metals such as Cu, Al, Fe and Ni. In this study, the valuable resource of Cu was selectively recovered from model AMD solution through membrane distillation and adsorption systems. Direct contact membrane distillation (DCMD) system enabled to concentrate the Cu concentration in AMD by more than 2.5 times while recovering 80% of high-quality water for reuse purposes. For adsorption, mesoporous silica material was used after multi-modification with Mn and amine grafting to enhance the adsorption capacity as well as selectivity for Cu. Under acidic conditions, heavy metals cannot be adsorbed on amine grafted SBA-15. Therefore, the pH of synthetic AMD (pH = 2.2) had to be adjusted to the 5.0-5.2 range, in order to enable adsorption of Cu on modified SBA-15 (this is to prevent protonation of amine groups grafted on prepared SBA-15). Moreover, an increase in pH helped to precipitate more than 99% of Fe and Al (predominant metals in AMD). Cu adsorption on modified SBA-15 was 24.53 mg/g for KOH-treated AMD. However, Cu adsorption on modified SBA-15 decreased by 26% (18.11 mg/g) for NaOH-treated AMD. Cu adsorption with modified SBA-15 significantly improved to 55.75 mg/g when the Cu concentration was concentrated by DCMD.

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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 2.08mmol/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 (2.01mmol/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 pH5. 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 pH5) as well as precipitation (above pH5). 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.

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Acid mine drainage (AMD) is a global environmental issue. Conventionally, a number of active and passive remediation approaches are applied to treat and manage AMD. Case studies on remediation approaches applied in actual mining sites such as lime neutralization, bioremediation, wetlands and permeable reactive barriers provide an outlook on actual long-term implications of AMD remediation. Hence, in spite of available remediation approaches, AMD treatment remains a challenge. The need for sustainable AMD treatment approaches has led to much focus on water reuse and resource recovery. This review underscores (i) characteristics and implication of AMD, (ii) remediation approaches in mining sites, (iii) alternative treatment technologies for water reuse, and (iv) resource recovery. Specifically, the role of membrane processes and alternative treatment technologies to produce water for reuse from AMD is highlighted. Although membrane processes are favorable for water reuse, they cannot achieve resource recovery, specifically selective valuable metal recovery. The approach of integrated membrane and conventional treatment processes are especially promising for attaining both water reuse and recovery of resources such as sulfuric acid, metals and rare earth elements. Overall, this review provides insights in establishing reuse and resource recovery as the holistic approach towards sustainable AMD treatment. Finally, integrated technologies that deserve in depth future exploration is highlighted.

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Acid mine drainage (AMD), an acidic effluent characterized by high concentrations of sulfate and heavy metals, is an environmental and economic concern. The performance of an integrated submerged direct contact membrane distillation (DCMD) - zeolite sorption system for AMD treatment was evaluated. The results showed that modified (heat treated) zeolite achieved 26-30% higher removal of heavy metals compared to natural untreated zeolite. Heavy metal sorption by heat treated zeolite followed the order of Fe > Al > Zn > Cu > Ni and the data fitted well to Langmuir and pseudo second order kinetics model. Slight pH adjustment from 2 to 4 significantly increased Fe and Al removal rate (close to 100%) due to a combination of sorption and partial precipitation. An integrated system of submerged DCMD with zeolite for AMD treatment enabled to achieve 50% water recovery in 30 h. The integrated system provided a favourable condition for zeolite to be used in powder form with full contact time. Likewise, heavy metal removal from AMD by zeolite, specifically Fe and Al, mitigated membrane fouling on the surface of the hollow fiber submerged membrane. The integrated system produced high quality fresh water while concentrating sulfuric acid and valuable heavy metals (Cu, Zn and Ni).

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