Phosphogypsum Leachates Research Articles

Advancing Phosphorus Recovery from Phosphogypsum Leachate with Solvent-Activated Nanofiltration Membrane

Phosphogypsum leachate is a phosphorus-rich wastewater posing a significant threat to the aquatic environment. The phosphorus in the leachate can be recovered via nanofiltration by allowing permeation of phosphorus while rejecting multivalent cations. However, the existing nanofiltration membranes face a significant challenge in addressing the inherent trade-off between the permeation of phosphorus and the rejection of multivalent cations, limiting the phosphorus recovery rate. Herein, solvent activation following interfacial polymerization between branched polyethyleneimine (PEI) and trimethyl chloride (TMC) was employed to simultaneously enhance the positive charge and enlarge its pore size. The MgCl2 rejection of the membrane increased from 93.7 ± 0.4% to 97.2 ± 0.3% and permeation also increased from 4.4 ± 0.1 L/(bar.m2.h) to 9.1 ± 0.4 L/(bar.m2.h) after activation, breaking the trade-off between rejection and permeation. Besides, in a mixture containing phosphorus and Mg2+, the activated membrane demonstrates a P/Mg2+ selectivity that is 6 times of the membrane before treatment, and surpassing the commercial and state-of-the-art membranes. Due to its high permeation and ideal P/Mg selectivity, the activated nanofiltration membrane has great potential for phosphorus recovery from phosphogypsum leachate.

Highly efficient recovery of phosphate and fluoride from phosphogypsum leachate: Selective precipitation and adsorption

Phosphogypsum, a typical by-product in the phosphorus chemical industry, could generate a large amount of leachate containing phosphate and fluoride in the process of rainfall and long-term stacking, which not only causes serious environmental pollution, but also leads to a waste of resources. In this study, a united treatment of calcium hydroxide precipitation and lanthanum zeolite (La-ZFA) adsorption was proposed to achieve the recovery of phosphate and fluoride from phosphogypsum leachate. In phosphogypsum, most phosphorus could be leached except P in the residual occurrence form, while for fluoride, only water-soluble F could be effectively leached. The optimum leaching amounts of phosphate and fluoride were 22.59 and 4.64 mg/g, respectively, at liquid-solid ratio of 400:1, leaching time of 120 min, pH of 6.0, particle size of >200 mesh (<0.075 mm), and leaching temperature of 25°C. Using Ca(OH)2 as the precipitant, the phosphate could be precipitated selectively from phosphogypsum leachate by controlling pH and time, and the concentrations of it decreased significantly to 0.29 mg/L at pH 10.0, with a removal efficiency of 99.48%. XRD, SEM and Visual MINTEQ software analysis proved that the main component of the precipitate was hydroxyapatite (Ca5(PO4)3(OH)). After P precipitation, a series of sorbents for fluoride were investigated, and La-ZFA sorbent was chosen and utilized to recover the fluoride from the leachate through a cyclic fixed-bed column. The efficiency of La-ZFA was basically not affected by the high concentration sulfate, and it can selectively adsorb fluoride from phosphogypsum leachate, leading to a final fluoride concentration of 0.29 mg/L in the effluent. The characterization demonstrated that fluoride might be adsorbed onto the La-ZFA via ligand exchange with hydroxy groups. The proposed method in this study is expected to sequentially recover phosphate and fluorine from the leachate of phosphogypsum, and it has great guiding significance for resource utilization and management of phosphogypsum.

Treating waste with waste: adsorption behavior and mechanism of phosphate in water by modified phosphogypsum biochar.

The use of green methods to treat industrial waste and waste reuse has become a key environmental issue. In order to achieve this goal, this study treated waste phosphogypsum (PG) and produced modified PG biochar to adsorb and remove phosphorus from PG leachate, so that the PG pollution problem was controlled. In this study, PG was modified with sodium carbonate (Na2CO3) to prepare a modified PG biochar that was used for the removal of phosphorus-containing wastewater. An X-ray diffraction (XRD) analysis of the modified PG revealed that the main component was calcium carbonate (CaCO3), and a suitable amount of modified PG could load calcium oxide (CaO) onto the biochar and improve its physical properties. The experimental results showed that the modified PG biochar had a maximum phosphorus adsorption capacity of 132mg/g. A further investigation of the mechanism of adsorption revealed the importance of electrostatic attraction and chemical precipitation, and it was found that the CaO in the modified PG biochar could effectively facilitate the conversion of phosphate to hydroxylapatite (Ca5(PO4)3OH) in water. The phosphorus removal rate from leachate obtained from a landfill containing PG was 99.38% for a specific dose of the modified PG biochar. In this study, a PG pollution control technology was developed to realize the goal of replacing waste with waste.

Assessment of metal(loid) and natural radionuclide pollution in surface sediments of an estuary affected by mining and phosphogypsum releases

The prolonged impact over the Tinto River estuary by both the significant pollution by acid mine drainage (AMD) affecting this river and the polluted releases from phosphogypsum (PG) piles has led to the severe environmental degradation of this ecosystem. The aim of this work was to assess the current environmental quality of the Tinto River estuary through the study of the spatial distribution of metal(loid)s and natural radionuclides in the surface sediments from the channel edge. The sediments contain mean concentrations 5–20 times higher than the background values for pollutants such as Zn, As, Cu, Pb, or U, and up to two orders of magnitude higher for P. The studied sediments are heavily polluted by toxic heavy metals and metalloids (Pb, Zn, Cu, and As) according to the US EPA guidelines. Most of the analyzed sediment samples are also strongly polluted by long-lived natural radionuclides, mainly U-isotopes and 210Pb with concentrations up to one order of magnitude higher than unpolluted sediments, mostly due to the contribution by the PG leachates. The enrichment factors (EF) were extremely high (EF > 50) for As and very severe enrichment (25 ≤ EF < 50) for P, Cd, Zn, Cu, and Pb.

Adsorption of rare earth elements (Ce3+, La3+, and Nd3+) and recovery from phosphogypsum leachate using a novel ZSM-5 zeolite

ZSM-5 zeolite is a multifunctional material highly efficient for adsorbing ions. Our ZSM-5 was synthesized by employing a nucleating gel as a structure-directing agent, followed by homogenization and hydrothermal treatment. The as-prepared ZSM-5 was physicochemically characterized to assess its properties. Next, the as-prepared zeolite was employed as an adsorbent to remove rare earth elements, REEs from synthetic solutions and real phosphogypsum leachate under batch mode operation. As expected, the ZSM-5 adsorbent was discovered to be highly microporous with abundant surface functionalities, which could positively impact REE adsorption. The adsorption data indicated a high affinity between ZSM-5 and all three REEs with rapid kinetics and high adsorption capacities. The modeling study suggested that the adsorption kinetic data were well fitted by Avrami-fractional order, and Liu described the equilibrium data. The maximum adsorption capacity for Ce3+, La3+, and Nd3+ were 99.42 mg g−1, 96.43 mg g−1, 118.10 mg g−1, respectively. Further, the thermodynamic analysis revealed that the interaction between ZSM-5 and Ce3+, La3+, and Nd3+ was favorable, spontaneous, and endothermic. The efficiency of ZSM-5 adsorbent was also studied in recovering several REEs from leachate of phosphogypsum wastes, and the data results proved its potency to do so. The findings reported in this work support the idea that ZSM-5 can be successfully used as an adsorbent to recover REEs from synthetic and real samples.

Efficient removal of phosphate and fluoride from phosphogypsum leachate by lanthanum-modified zeolite: Synchronous adsorption behavior and mechanism

Phosphogypsum is a common large-tonnage by–product in phosphorous chemicals industry, its stacking not only causes severe environmental problems, but also leads to a serious waste of phosphate and fluoride resources. The objective of this study was to tackle the recycling treatment of phosphogypsum leachate by using a highly efficient adsorbent lanthanum hydroxide-modified zeolite (LMZ). The adsorption behaviors of phosphate and fluoride by LMZ in the coexisting system under static and dynamic conditions were studied. And further, the competitive adsorption mechanism involved was analyzed. The results showed that LMZ possessed excellent adsorption performance toward both phosphate and fluoride in the single system, but the fluoride adsorption capacity decreased by 57.9 % in the coexisting system, with no change in phosphate adsorption. In the competitive adsorption process, ligand exchange interaction on La active sites contributed most to phosphate adsorption, while fluoride could be adsorbed onto LMZ via electrostatic attraction, surface precipitation with Al sites, and hydrogen bonds with hydroxyl groups in La−OH and P−OH. In actual phosphogypsum leachate, the removal of phosphate had priority over the removal of fluorine. Under continuous adsorption condition, the concentration of phosphorus and fluoride could be decreased to below 0.5 and 1.0 mg/L, respectively, meeting the safe concentration in drinking water. This study promotes the application of La–based adsorbents in the treatment of phosphogypsum leachate, and provides a green and sustainable strategy toward practical phosphorus and fluorine recovery.

Recovery and concentration of Eu(III) from phosphogypsum leachate using ouricuri endocarp

Ouricuri endocarp was utilized as a biosorbent for the recovery of europium (Eu(III)) from aqueous solutions and rare earth elements (REEs) from authentic leachate derived from phosphogypsum, which encompasses various REEs. Various characterization techniques were applied to analyze the physicochemical and adsorptive properties of the biosorbent. The results indicate that the adsorption kinetic data conform well to the pseudo-first-order model, while the Liu model describes the equilibrium data well. Ouricuri endocarp and Eu interactions are favorable and spontaneous. The maximum adsorption capacity for Eu(III) is determined to be 22.9 mg/g according to the Liu model. Based on experimental results and adsorbent characteristics, the proposed adsorption mechanisms between ouricuri endocarp and Eu include ion exchange and electrostatic interactions as the primary mechanisms. The Eu(III) recovery is also feasible as a continuous flow process demonstrating inclined breakthrough curves and lower values of the length of the mass transfer zone. Ouricuri endocarp demonstrates its selectivity for recovering various REEs from authentic phosphogypsum leachate. It achieves a 98% recovery rate for Eu and approximately 60% for Ce, La, and Nd, affirming its efficacy under real-world conditions. Finally, concentration of REE was done by ashing loaded ouricuri endocarp, and a solid with around 34% (in weight) of REE is obtained.

Boosting synergistic recovery of ammonia nitrogen and phosphate from phosphorus chemical wastewater by co-pyrolyzing the biomass and magnesite

In this study, biomass was co-pyrolyzed with the low-cost magnesite to prepare nano-MgO loaded biochar (n-MgO/biochar) composites for the simultaneous recovery of NH4+-N and PO43--P consisting in wastewater. It was found from the outcomes that the addition of biomass effectively reduced the pyrolysis temperature of magnesite, and the dispersion of biochar promoted the reactive activation of nano-scale MgO. The nano-MgO could provide Mg2+ and OH− simultaneously for the efficient recovery of NH4+-N and PO43--P. At a pH of approximately 9 and an N/P/Mg molar ratio of 1:2:1.5, the NH4+-N and PO43--P in the experimental wastewater were recovered by 93.7 % and 84.8 %, respectively. Mechanism analysis revealed that chemical adsorption, with the main product being MgNH4PO4·6H2O, predominantly controlled the recovery process. Furthermore, n-MgO/biochar demonstrated a successful recovery of NH4+-N and PO43--P consisting in the complex phosphogypsum leachate. What’s more, NaH2PO4, n-MgO/biochar/P, and raw phosphogypsum leachate could all serve as effective phosphorus sources for recovering NH4+-N consisting in nitrogenous wastewater with phosphorus deficiency. Conclusively, this study provides an alternative method for the simultaneous recovery of NH4+-N and PO43--P consisting in the wastewater.

An Integrated Precipitation–Electrodeposition–Electrodialysis Strategy for Efficient Close-Loop Recovery of Multiple Anions from Phosphogypsum Leachate

An Integrated Precipitation–Electrodeposition–Electrodialysis Strategy for Efficient Close-Loop Recovery of Multiple Anions from Phosphogypsum Leachate

Assessing the hepatotoxicity of phosphogypsum leachate in zebrafish (Danio rerio)

The improper disposal of large amounts of phosphogypsum generated during the production process of the phosphorus chemical industry (PCI) still exists. The leachate formed by phosphogypsum stockpiles could pose a threat to the ecological environment and human health. Nevertheless, information regarding the harmful effects of phosphogypsum leachate on organisms is still limited. Herein, the physicochemical characteristics of phosphogypsum leachate were analyzed, and its toxicity effect on zebrafish (Danio rerio), particularly in terms of hepatotoxicity and potential mechanisms, were evaluated. The results indicated that P, NH3-N, TN, F−, As, Cd, Cr, Co, Ni, Zn, Mn, and Hg of phosphogypsum leachate exceeded the V class of surface water environmental quality standards (GB 3838–2002) to varying degrees. Acute toxicity test showed that the 96 h LC50 values of phosphogypsum leachate to zebrafish was 2.08 %. Under exposure to phosphogypsum leachate, zebrafish exhibited concentration-dependent liver damage, characterized by vacuolization and infiltration of inflammatory cells. The increased in Malondialdehyde (MDA) content and altered activities of antioxidant enzymes in the liver indicated the induction of oxidative stress and oxidative damage. The expression of apoptosis-related genes (P53, PUMA, Caspase3, Bcl-2, and Bax) were up-regulated at low dosage group and down-regulated at medium and high dosage groups, suggesting the occurrence of hepatocyte apoptosis or necrosis. Additionally, phosphogypsum leachate influenced the composition of the zebrafish gut microbiota by reducing the relative abundance of Bacteroidota, Aeromonas, Flavobacterium, Vibrio, and increasing that of Rhodobacter and Pirellula. Correlation analysis revealed that gut microbiota dysbiosis was associated with phosphogypsum leachate-induced hepatotoxicity. Altogether, exposure to phosphogypsum leachate caused liver damage in zebrafish, likely through oxidative stress and apoptosis, with the intestinal flora also playing a significant role. These findings contribute to understanding the ecological toxicity of phosphogypsum leachate and promote the sustainable development of PCI.

Sequence closed-loop recovery of fluoride, phosphate, and sulfate anions from phosphogypsum leachate via precipitation-electrodialysis-crystallization approaches

Phosphogypsum (PG) is a large-scale industrial by-product generated during the production of phosphoric acid, typically being deposited in landfills worldwide. The leaching of fluoride (F−), phosphate (PO43−), and sulfate (SO42−) anions from PG into water bodies through rainfall results in significant environmental pollution. Herein, we propose a stepwise precipitation combined with electrodialysis and crystallization strategy for efficient recovery and valorization of multiple anions from PG leachate. Our method demonstrates effectiveness both theoretically and practically. Consequently, fluoride anions were precipitated as CaF2 and Ca5(PO4)3F at pH 4.7, with a recovery rate of 98.80 %; phosphate anions as MgNH4PO4·H2O at pH 8.5, with a recovery rate of 99.91 %; and sulfate anions through electrodialysis and crystallization with a recovery efficiency of 99.89 %, ensuring effluent met discharge standards. In addition, the concentrated sulfate-rich solution was employed for electrochemical production of persulfate, yielding ammonium persulfate salts after cooling crystallization. Our integrated approach for multiple anion recovery from PG leachate offers significant environmental and economic benefits, providing valuable insights and references for future research and practical production.

Adsorption of rare earth elements on a magnetic geopolymer derived from rice husk: studies in batch, column, and application in real phosphogypsum leachate sample.

There is a growing need to develop new strategies for rare earth element (REE) recovery from secondary resources. Herein, a novel approach to utilize biogenic silica (from rice husk) and metakaolin was employed to fabricate magnetic geopolymer (MGP) by incorporating metallic iron. The fabricated MGP adsorbent material was used to uptake Ce3+, La3+, and Nd3+ from synthetic solutions and real phosphogypsum leachate in batch and column modes. The MGP offers a negatively charged surface at pH above 2.7, and the uptake of REEs rises from pH 3 to 6. The kinetic study validated that the kinetics was much faster for Nd3+, followed by La3+ and Ce3+. A thermodynamic investigation validated the exothermic nature of the adsorption process for all selected REEs. The desorption experiment using 2mol L-1 H2SO4 as the eluent demonstrated approximately 100% desorption of REEs from the adsorbent. After six adsorption-desorption cycles, the MGP maintained a high adsorption performance up to cycle five before suffering a significant decrease in performance in cycle six. The effectiveness of MGP was also assessed for its applicability in recovering numerous REEs (La3+, Ce3+, Pr3+, Sm3+, and Nd3+) from real leachate from phosphogypsum wastes, and the highest recovery was achieved for Nd3+ (95.03%) followed by Ce3+ (86.33%). The operation was also feasible in the column presenting suitable values of the length of the mass transfer zone. The findings of this investigation indicate that MGP adsorbent prepared via a simple route has the potential for the recovery of REEs from synthetic and real samples in both batch and continuous operations modes.

Simplification of the pretreatment method for phosphate oxygen isotope measurement in phosphogypsum leachate

The stacking of phosphogypsum has caused considerable phosphorus pollution in water bodies near phosphogypsum yards through surface runoff and underground infiltration. The phosphate oxygen isotope (δ18Op) tracing method has served as a valuable tool for tracing phosphorus pollution in water. However, the existing δ18Op enrichment and purification methods are complex, costly, and inefficient for phosphate recovery, particularly for phosphogypsum leachate with complex compositions. Herein, a simplified and optimized pretreatment method for δ18Op measurement in phosphogypsum leachate was developed. Zirconium/polyvinyl alcohol (Zr/PVA) gel beads showed good selectivity for phosphate enrichment from water at different initial phosphate concentrations with appropriate Zr/PVA dosage. The optimal enrichment pH value was <7, and the concentrated phosphate on the Zr/PVA gel beads could be effectively eluted in an alkaline environment. Compared with the traditional Fe or Mg coprecipitation enrichment methods, impurities in the solution showed no obvious adverse effects on the phosphate enrichment process. Further, the phosphate solution eluted from the Zr/PVA gel beads was purified by a simple adjustment of the pH instead of cation exchange in the traditional purification process. Magnesium ions in the solution could be completely removed when the pH ranged from 3.17 to 6.15, and the phosphate recovery rate could reach 98.66% when the eluent pH was 5.02. Fourier-transform infrared spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy revealed that similar to traditional pretreatment method, the proposed method can obtain high-purity Ag3PO4 solids for δ18OP measurement and no isotope fractionation of δ18OP was observed. Therefore, this study provides a promising and reliable pretreatment method for δ18OP measurement, especially in complex phosphogypsum leachate.

Evolution of the waste generated along the cleaning process of phosphogypsum leachates

“The generation of acidic leachates from phosphogypsum (PGL) stacks is a global problem due to their high pollutant concentrations (As, Cr, Cd, Cu, Ni, Zn, F-, PO43-, SO42-, 210Po and 238,234U). The cleaning treatment of the PGL by neutralization with alkaline reagents is a proper option for removal of pollutants by (co)-precipitation. This study is focused on the characterization of the wastes generated along the cleaning process of PGL using CaCO3 and Ca(OH)2 with the aims of diagnosis for their valorization. In addition, a chemical modelling was performed to obtain a general guide on the precipitation behavior (cleaning) of the chemical species when the pH is increased. The main finding was that the fluorine is removed from dissolution as fluorite at pH around 3, precipitating with some gypsum. Nevertheless, calcium phosphate dominates the precipitated phase during the alkaline treatment, where monetite and brushite are the prevailing species formed at neutral pH range and fluorapatite in more basic conditions. These species contain very high concentrations of toxic chemical species and 238U-series radionuclides (mainly 238U-isotopes and 210Pb). Therefore, it is needed to design a valorization process for these two generated wastes, which could contribute to the circular economy and the improvement of the environmental conditions of the PG stacks surroundings.”

Recovery of Ce and La from phosphogypsum leachate by adsorption using grape wastes.

The present research aimed to evaluate the use of grape stalk in the adsorption of lanthanum and cerium to identify the best operating conditions enabling the application of the bioadsorbent in REEs leached from phosphogypsum. The grape stalk was characterized and showed an amorphous structure with a heterogeneous and very porous surface. Also, it was possible to identify the groups corresponding to carboxylic acids, phenols, alcohols, aliphatic acids, and aromatic rings. The pH effect study showed that the adsorption process of La3+ and Ce3+ ions was favored at pH 5.0. The adsorption kinetics followed the pseudo-second-order model. In just 20 min, 80% saturation was reached, while equilibrium was reached after 120 min. The adsorption isotherms were appropriately adjusted to the Langmuir model, and the maximum adsorption capacities were obtained at 298 K, which were 35.22 mg g-1 for La3+ and 37.99 mg g-1 for Ce3+. Furthermore, the adsorption process was favorable, spontaneous, and exothermic. In the study's second phase, phosphogypsum was leached with a sulfuric acid solution. Then, the adsorption of REEs was carried out under the experimental conditions of pH after leaching and pH 5.0 (adjustment carried out with sodium hydroxide solution) at 298 K for 120 min and with adsorbent dosages of 1 and 5 g L-1. This process resulted in removal percentages above 95% for the most abundant REEs, such as neodymium, lanthanum, and cerium, at pH 5.0 and a dosage of 5 g L-1, demonstrating the effectiveness of the bioadsorbent used. These results indicate the potential of using grape residue as a promising bioadsorbent in recovering rare earth elements from phosphogypsum leachate.

Vine pruning waste-based activated carbon for cerium and lanthanum adsorption from water and real leachate

In this study, vine pruning wastes (VPW) were used as raw material to develop an alternative activated carbon (VPW-AC) for adsorbing and concentrating rare earth elements cerium (Ce(III)) and lanthanum (La(III)) from synthetic and real leachate solutions. The Ce and La adsorption studies evaluated the effects of VPW-AC dosage, pH, contact time, rare earth initial concentration, and temperature. The VPW-AC adsorbent was subjected to many physicochemical characterization methods to correlate and understand its adsorptive performance. The characterization data indicate a carbonaceous adsorbent with a specific surface area of 467 m2/g. Zeta potential indicates a material with a negatively charged surface at a pH higher than 3.1, which is extremely beneficial to cations removal. For both rare earths elements (REEs), the adsorption capacity increases with the increase of the pH, reaching its maximum at pH 4–6. The kinetic data are well fitted by Avrami-fractional order, while the Liu model agreeably fits equilibrium data. The maximum adsorption capacities for Ce(III) and La(III) are 48.45 and 53.65 mg/g at 298 K, respectively. The thermodynamic studies suggest that the adsorption process is favorable, spontaneous, and exothermic for both REEs. Pore filling, surface complexation, and ion exchange are the dominant mechanisms. Finally, the VPW-AC was subjected to the recovery of REEs from real phosphogypsum leachate, and it is proved that it can be successfully used to recover REEs in a real process.

Synergistic harmless treatment of phosphogypsum leachate wastewater with iron-rich electrolytic manganese residue and electric field

In the iron-rich electrolytic manganese residue (IREMR) and phosphogypsum leachate wastewater (PLW), there are high levels of Mn2+, NH4+-N, F−, and PO43− pollutants which severely contaminate the surrounding environment. This study focuses on a synergistic and environmentally friendly treatment of PLW using IREMR and an electric field. During the mixed leaching process, with a mass ratio of IREMR to PLW of 1:25, a reaction temperature of 25 °C, a leaching pH of 3.0, and a reaction time of 30 min, the concentrations of Mn2+ PO43−, NH4+-N, and F− in the mixed leaching wastewater were measured to be 1235.49 mg/L, 1507.97 mg/L, 700.15 mg/L, and 146.76 mg/L, respectively. In the pollutant precipitation removal process, with a pH of 9.5 in the mixed leaching wastewater, a current density of 10 mA/cm2, a reaction temperature of 35 °C, and a reaction time of 45 min, the removal efficiencies of Mn2+, PO43−, NH4+-N, and F− were found to be 99.81 %, 99.86 %, 58.37 %, and 99.90 %, respectively. The removal mechanism indicates that Mn2+, F−, PO43−, and NH4+-N were primarily eliminated through the formation of Mn(OH)2, Mn3(PO4)2·2H2O, CaF2, MnF2, and Mg(NH4)PO4·6H2O. This research offers a new approach for the resource utilization and environmentally safe treatment of PLW.

Effect of alkaline leaching of phosphogypsum on sulfate reduction activity and bacterial community composition using different sources of anaerobic microbial inoculum

Phosphogypsum (PG), a by-product of the phosphate industry, is high in sulfate, (SO42−), which makes it an excellent substrate for sulfate-reducing bacteria (SRB) to produce hydrogen sulfide. This work aimed to optimize SO42− leaching from PG to achieve a high biological reduction of SO42− and generate high sulfide concentrations for subsequent use in the biological recovery of elemental sulfur. Five SRB consortia were isolated and enriched from: IS (Industrial sludges), MS (Marine sediments), WC (Winogradsky column), SNV (petroleum industry sediments) and PG (stored Phosphogypsum). The five consortia showed reduction activity when using PG leachate (with water) as source of SO42− and lactate, acetate, or glucose as the electron donor. The highest reduction rate (81.5 %) was registered using lactate and the IS consortium (81.5 %) followed by MS (79 %) and PG (71 %). To enhance the concentration of leached SO42− from PG for future utilization with the isolated consortia, PG was treated with NaOH solutions (2 % and 5 %). SO42− release of 97 % was achieved with a 5 % concentration and the resulting leachate was further diluted to target a SO42− concentration of 12.4 g·L−1 for utilization with the isolated consortia. Compared to water leachate, a significantly higher reduction rate was registered (2 g·L−1 of SO42) using the IS consortium, demonstrating limited inhibition effect of sulfide− concentration on SRB functionalities. Moreover, metagenomic analysis of the consortia revealed that using PG as a source of SO42− increased the abundance of Deltaproteobacteria, including known SRB like Desulfovibrio, Desulfomicrobium, and Desulfosporosinus, as well as novel SRB genera (Cupidesulfovibrio, Desulfocurvus, Desulfococcus) that showed, for the first time, significant potential as novel sulfate-reducers using PG as a SO42− source.

Adsorptive behavior of the rare earth elements Ce and La on a soybean pod derived activated carbon: Application in synthetic solutions, real leachate and mechanistic insights by statistical physics modeling

In this study, we aimed to produce a sustainable and efficient powdered activated carbon (SP-AC) and evaluate its adsorptive abilities to uptake and recover rare earth elements (REEs) from synthetic solutions containing lanthanum (La(III)) and cerium (Ce(III)), and real leachate, from phosphogypsum, containing several REEs. The adsorbent material was subjected to several characterization techniques to understand its physicochemical and adsorptive properties. The characterization results indicated that the activated carbon prepared in this work possesses a specific surface area, pore volume, and average pore diameter of 614 m2g−1, 0.121 cm3g−1, and 3.65 nm, respectively. Interestingly, the adsorbent material exhibited a highly negatively charged surface which was extremely beneficial for La(III) and Ce(III), which are positively charged and therefore were easily attracted to each other. The kinetic data were well fitted by pseudo-second-order, while the Liu model agreeably fitted equilibrium data. The maximum adsorption capacities for Ce(III) and La(III) were 107.7 and 127.2 mg g−1 at 298 K, respectively. The thermodynamic data indicated that the adsorption systems between SP-AC and both REEs were favorable, spontaneous, and exothermic. The adsorption mechanisms between SP-AC and the two REEs were proposed based on the experimental results, adsorbent characteristics, and statistical physics approach. Pore filling and ion exchange were the main mechanisms, although surface complexation was also involved. Finally, the SP-AC was employed to recover many REEs from real phosphogypsum leachate, demonstrating that SP-AC can selectively recover REEs in the real process.

Phosphorus recovery and resource utilization from phosphogypsum leachate via membrane-triggered adsorption and struvite crystallization approach

Phosphorus pollution from phosphogypsum (PG) leachate has caused severe problems in the water environment and ecology. Efficient phosphate recovery and resource utilization techniques are crucial as they can aid the phosphorus pollution problem and recover the scarcity of phosphorus resources. Herein, we developed a highly efficient phosphorus recovery strategy from PG leachate by integrating the ZrO2 membrane-triggered adsorption technique with the struvite crystallization process. More than 89.23% of the phosphorus anions in the PG leachate can be recovered via membrane-triggered adsorption. With the concentrated phosphate anions washed from membrane adsorption, the phosphate anions can be further employed for struvite crystallization, and an overall phosphorus recovery efficiency of 59.36% can be achieved. The obtained fine struvite product is of high purity, with NH4MgPO4·6H2O weight ratio of up to 89.83%. The novel strategy developed here demonstrates a green and sustainable strategy toward phosphorus recovery from the PG or PG-polluted groundwater or surface water leachate, which could be applied to practical phosphorus recovery and struvite fertilizer production. The commercialization of this strategy will shed light on the emergency PG pollution control at the YangtzeRiver upstream area.