Nitric Acid Leaching Research Articles

Low-carbon upcycling of spent anode graphite: Integrating graphene and dislocations for sustainable lithium/potassium storage

Nowadays, the recycling and sustainable energy storage techniques of spent rechargeable batteries have garnered tremendous passion and scrutiny on account of the escalating environmental crisis and energy shortage. This study presents a facile and green method for upcycling graphite from spent lithium-ion batteries. Unlike conventional high-temperature calcination approaches, our technique leverages low-temperature annealing at 350 °C in air to treat graphite from spent anodes after diluted nitric acid (5 mol/L) leaching. This craft is characterized by its simplicity, safety, and cost-effectiveness. Experimental results reveal that the upcycled graphite stimulated both lithium and potassium storage. Specifically, the upcycled graphite maintains the boosting capacity of 415.6 mAh/g after 180 cycles in lithium-ion cells. This stellar performance is attributed to the formation of graphene sheets, abundant dislocations, and the preservation of ample interlayer spacing. Our method substantially reduces energy consumption and environmental pollution. Future research will further explore the applications of upcycled graphite in other types of ion batteries and mitigate its environmental impacts.

Effect of pH neutral on the separation of nickel and cobalt from laterite leaching solution using cyanex 272

Abstract Nickel and cobalt are the most common elements in the earth’s crust that naturally occur in laterite ores. Nickel and cobalt from laterite ores are recovered as products such as mixed hydroxide precipitate (MHP) and mixed sulphide precipitate (MSP). This research focuses on how the nickel laterite leach solution can be processed directly for solvent extraction without going through the precipitation stage. The nitric acid leach solution obtained from the laterite ore is used to extract nickel and cobalt. A cyanex 272 extractant and kerosene mixture will be used as an organic solvent for direct extraction. The raw material used was Indonesian laterite ore from Halmahera Island, which contained Ni (1.72%), Co (0.155%), Fe (26.17%), and other minor elements. The effect of pH in a neutral condition was investigated on the extraction efficiency, distribution coefficient, and separation factor. Nitric acid (1M) was applied as the leaching reagent. The variables include pH variations (6.8; 7.0; 7.2; 7.4; 7.6), 20% cyanex 272, and O/A ratio (1:1/v:v) at 20 minutes with a stirring speed of 500 rpm. Optimum results were obtained at pH 7.4 variation with an extraction efficiency of 69.26% for cobalt and 0% for Ni, respectively. At these optimum conditions, the highest distribution coefficient value is the element cobalt at pH 7.4, and the result is 2.253 with a separation factor (∞). The optimum condition focuses on removing cobalt from the organic phase, not nickel.

Copper leaching from ultrasonically treated milled waste printed circuit boards: investigation of parameters optimization and kinetics.

Waste printed circuit boards (WPCBs) encompass abundant metals (gold, silver, and copper), along with other harmful materials including brominated epoxy resins, plastics, and heavy metals (lead, mercury, and cadmium). Direct burning and landfilling of WPCBs may cause severe health issues and impair the environment. Therefore, sustainable treatment of WPCBs is necessary to recover valuable metals and remove hazardous materials before disposal. The present work investigates the separation of copper-rich metallic fractions from the WPCBs by the combination of hammer milling and ultrasonic irradiation. Initially, discarded mobile phone PCBs are pre-processed and shortened into 1 × 1 cm2. Downscaled WPCBs are fed into the hammer mill to obtain the fine ground powder. The Powdered WPCBs are further processed through ultrasonic treatment to acquire metal-rich fraction. XRD, SEM-EDS, and ICP/AAS analysis revealed that the current technique can efficiently separate the metal-rich fraction without using toxic solvents. Results show the enhancement of copper fraction from 42.73 to 87 wt. % after ultrasonic treatment of WPCBs ground powder. Further, nitric acid leaching has been implemented to metal-rich fractions, and the parameters have been optimized for copper leaching with the assistance of response surface methodology (RSM) of the design of experiments (DOE). Quantitative dissolution (98.96%) of copper occurred using 3.5M nitric acid within 3h at 30°C with 50 GPL pulp density and 500rpm agitation speed. Finally, the kinetics of the leaching process were studied to conform the kinetics model. Moreover, the activation energy for diffusion (19.075kJ/mole) and reaction kinetics model (13.29kJ/mole) has also been calculated. The low energy consumption due to room temperature pre-treatment and effective leaching ensures the industrial feasibility of the proposed process.

A thermogravimetric analysis of residual char formation by gilsonite-filled, polyfurfuryl alcohol composites: acid treatment of gilsonite

Gilsonite (GLS), a natural bitumen containing a considerable amount of asphaltenes, is expected to leave heavy char after pyrolysis; however, its high potential as an efficient filler to enhance the thermal properties of composite materials is surprisingly neglected throughout the literature. On the other hand, polyfurfuryl alcohol (PFA) has attracted much attention as a thermosetting resin due to its excellent char-leaving characteristics, the renewable nature of the monomer(s), and high accessibility at an affordable cost. This study aimed to investigate the thermal stability and char-forming performance of composites made of a PFA resin matrix filled with chemically modified GLS. To modify the ash and sulfur contents of GLS, the nitric acid leaching process was performed according to a D-optimal experimental design approach. The nitric acid concentration (10, 20, and 30 wt.%), treatment time (30, 75, and 120 min), and reaction temperature (30 °C, 50 °C, and 70 °C) were set as the input variables. The morphology (SEM), chemical structure (FTIR), thermal stability (TGA), sulfur content, and ash content of the GLS particles were characterized before and after acid treatment. Thermogravimetric analysis revealed the lowest ash content for GLS after treatment with 10 wt.% acid conc. at 75 °C for 75 min. The nitric acid concentration, reaction temperature, and time were the most influential parameters for improving the ash content of GLS according to their order of appearance. In addition, the inorganic form of sulfur, pyrite, was separated through the acid leaching process. Then, the PFA resin matrix was filled with modified GLS particles at different weight percentages (5, 10, 15, and 20 wt.%) and cured in the presence of an acid catalyst. The thermal stability of the PFA resin was negatively affected by the presence of GLS, probably due to oxidation reactions and disruption of the integrity of the resin structure.

Development of complete hydrometallurgical processes for gold recovery from ICs and CPUs using ionic liquids

Integrated circuits (ICs) and central processing units (CPUs), essential components of electrical and electronic equipment (EEE), are complex composite materials rich in recyclable high-value strategic and critical metals, with many in concentrations higher than in their natural ores. With gold the most valuable metal present, increase in demand for gold for EEE and its limited availability have led to a steep rise in the market price of gold, making gold recycling a high priority to meet demand. To overcome the limitations associated with conventional technologies for recycling e-waste, the use of greener technologies (ionic liquids (ILs) as leaching agents), offers greater potential for the recovery of gold from e-waste components. While previous studies have demonstrated the efficiency and feasibility of using ILs for gold recovery, these works predominantly concentrate on the extraction stage and often utilise simulated solutions, lacking the implementation of a complete process validated with real samples to effectively assess its overall effectiveness. In this work, a simulated Model Test System was used to determine the optimal leaching and extraction conditions before application to real samples. With copper being the most abundant metal in the e-waste fractions, to access the gold necessitated a two-stage pre-treatment (nitric acid leaching followed by aqua regia leaching) to ensure complete removal of copper and deliver a gold-enriched leach liquor. Gold extraction from the leach liquor was achieved by liquid-liquid extraction using Cyphos 101 (0.1 M in toluene with an O:A = 1:1, 20 °C, 150 rpm, and 15 min) and as a second process by sorption extraction with loaded resins (Amberlite XAD-7 with 300 mg of Cyphos 101/g of resins at 20 °C, 150 rpm and 3 h). In both processes, complete stripping and desorption of gold was achieved (0.5 M thiourea in 0.5 M HCl) and gold recovered, as nanoparticles of purity ≥95%, via a reduction step using a sodium borohydride solution (0.1 M NaBH4 in 0.1 M NaOH). These two hydrometallurgical processes developed can achieve overall efficiencies of ≥95% for gold recovery from real e-waste components, permit the reuse of the IL and resins up to five consecutive times, and offer a promising approach for recovery from any e-waste stream rich in gold.

Collaborative extraction of valuable components from saprolitic laterite ore through two-stage nitric acid leaching

Saprolitic laterite ore (SLO) is an important Ni resource that also contains high Mg and a small amount of Sc, but traditional extraction techniques cannot achieve the comprehensive utilization of valuable components, especially Mg and Sc. In this work, a new process was proposed to treat SLO through the application of an HNO3 medium. First, E-pH analysis showed that serpentine and part of iron oxide are easily destroyed, and Ni and Co embedded in silicate and Fe-bearing minerals can be also leached. Subsequently, Ni, Mg, Co, and Sc can be efficiently extracted under the HNO3 concentration of 240 g/L, 90 ℃, L/S of 5:1, 2 h, and 200 r/min. Relevant characterization confirmed that serpentine and goethite were almost completely dissolved after leaching. However, magnetite and its alteration intermediates have relatively stable properties and cannot be destroyed. To reduce acid consumption, the leach liquor was supplemented with HNO3 for two-stage leaching. Efficient extraction of valuable metals can be achieved again with the supplemented HNO3 concentration of 192 g/L. A two-stage leaching process can save 120 kg HNO3/t-ore. Finally, a technical route including two-stage HNO3 leaching, adding MgO to adjust pH, and pyrolysis of Mg(NO3)2 to regenerate HNO3 and MgO was suggested.

Atmospheric hydrochloric and nitric acid leaching of a limonite ore from the Wolo mine area, Southeast Sulawesi, Indonesia

The atmospheric acid leaching studies of a limonite ore sample from the Wolo mine area, Southeast Sulawesi, Indonesia, have been performed using hydrochloric acid (HCl) and nitric acid (HNO3). The objectives of these studies were to compare the leaching degree of metals (Ni, Co, Fe, and Al) and to analyze the dissolution behavior of minerals under different acid concentrations. Mineralogical characterization of the ore sample was conducted using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction, whereas chemical composition was determined by X-ray fluorescence (XRF) spectrometry and atomic absorption spectroscopy (AAS), respectively. An atmospheric leaching test was done with the variables of acid concentration, leaching duration of 90 min, and leaching temperature of 100℃. Limonite ore samples contain goethite, gibbsite, talc, quartz, and lizardite. It was revealed that as much as 92.22% of Ni and 90.14% of Fe could be leached using 3 M HCl, whereas only 63.14% of Ni and 38.74% of Fe could be extracted from limonite ore using 3 M HNO3. The higher leaching degree of Fe in HCl indicates low selectivity with Ni, which might contaminate pregnant leach solution (PLS), leading to further complications in the purification process. Results of the leaching experiment show that goethite was more easily dissolved in HCl than in HNO3.

Parameters effect and optimization on calciner for treating magnesium salt based on computational fluid dynamics

The magnesium salt Mg(NO3)2·2H2O from laterite nickel ore nitric acid leaching process can be reused by thermal decomposition using calciner. To improve the performance of the calciner, a new numerical model integrating the gas-particle hydrodynamics and the particle pyrolysis reaction was established by Euler-Lagrange approach. In particular, the particle size variation caused by pyrolysis reaction was considered to accurately describe the gas-particle hydrodynamics. The particle pyrolysis model was developed to realize the interphase mass transfer. The P-1 model was modified to realize interphase radiation heat transfer. Then, the influence of different parameters on the thermal decomposition processes was discussed by using the established model. Finally, the optimal conditions for Mg(NO3)2·2H2O thermal decomposition were determined via response surface optimization analysis. The results show that the thermal decomposition of Mg(NO3)2·2H2O can be improved by increasing the initial hot gas temperature, reaction zone height, and decreasing treatment capacity of Mg(NO3)2·2H2O. The degree of influence of each parameter on thermal decomposition follows the order of initial hot gas temperature > treatment capacity of Mg(NO3)2·2H2O > reaction zone height. The decomposition rate of 99.99 % is obtained at optimized conditions of initial hot gas temperature 1111 K, Mg(NO3)2·2H2O treatment capacity 251 kg/h and reaction zone height 9 m.

Application of MLR Method and Pearson Correlation on Nickel Extraction from Laterite Using Nitric Acid

Indonesia is a country rich in laterite mining especially in Celebes island and northern Moluccas. Laterite is a mineral rich with precious nickel. Nitric acid leaching has been used for nickel extraction from laterite under the influence of nitric acid concentration (2.0 M, 4.0 M, and 6.0 M) and leaching temperature (65oC, 70oC, and 75oC) during 60 min. at 300 rpm. The preliminary study aims to apply multiple linear regression (MLR) method to examine the dominant effect between acid concentration and leaching temperature on nickel extraction, and also Pearson correlation to study significant correlation between the variables involved (acid concentration, leaching temperature, and nickel concentration). The method and results is related to acid leaching at varied temperature set up as predictors and nickel concentration as dependent variable in the MLR equation using the enter method. The MLR method showed that acid concentration gave significant effect on nickel concentration, however, the leaching temperature showed no significant effect on nickel extraction at t ≤ 0.05. The Pearson correlation showed acid concentration correlated significantly with nickel concentration. The Kolmogrov-Smirnov (K-S) test showed normality for distribution of nickel concentration. The acid leaching method is potential for nickel extraction from laterite using extensive range of acid concentrations and leaching temperatures to improve nickel extraction.

Determination of metal fractions and rare earth anomalies in red mud: the case of bauxite mining district of Seydişehir (Turkey)

A three-step sequential extraction was carried out by modified BCR approach for fractionation of metals, including rare earths in red mud. Acetic acid leaching, hydroxylamine hydrochloride + nitric acid leaching, hydrogen peroxide + acid ammonium acetate leaching, and orthophosphoric + nitric acid digestion in microwave were performed to determine ion exchangeable (F1), reducible (F2), oxidizable (F3), and residual (F4) fractions of metals, respectively. Accordingly, the highest readily soluble phases were obtained for Ca, Na, and K, while the reducible were Al, Zn, Cu, and Li. Rare earth elements (REEs) except for Eu were mostly identified in residual fraction. Most of Eu (88.7%) was detected in the reducible fraction, while the negligible part in residual. Chondrite normalization was implemented for obtaining REE anomalies. The remarkable Eu and Gd negative anomaly differences were determined between the red mud and its origin, Mortaş bauxite. The LREE to HREE ratio and LaN/YbN scores of 8.42 and 7.82, respectively indicated the LREE enrichment to HREE. By performing multivariate analysis, six and five-group clusters were obtained for REEs and non-REE metals in terms of fractional distribution, proving the easier release potential of Eu, La, Gd, K, Na, and Ca.

RESEARCH AND DEVELOPMENT OF MATHEMATICAL MODELS FOR THE PROCESS OF PROCESSING GOLD, COPPER-CONTAINING CONCENTRATES

The paper discusses the problems of increasing the efficiency of processing gold- and copper-containing ores of the Taror deposit. A flotation enrichment scheme for the studied ores and a phase analysis of the flotation concentrate have been developed, and the leaching of honey and gold from the concentrate of the studied deposit has been studied. The main kinetic patterns of nitric acid decomposition of flotation concentrate from the Taror deposit have been studied. The optimal conditions for opening gold- and copper-containing concentrates with nitric acid were found: nitric acid concentration – 400 g/dm3; process duration – 120 minutes; S:I ratio = 1:5. Based on experimental data, a mathematical model has been proposed for determining the degree of extraction of this component during nitric acid leaching of gold- and copper-containing flotation concentrates from the Taror deposit. Based on scientific research, a basic scheme for processing gold- and copper-containing ores from the Taror deposit has been developed.

Use of Plackett–Burman Statistical Design to Study Factors Acting on the Nitric Acid Leaching of Rare Earth Elements from Moroccan Phosphogypsum

This work is an attempt to understand and optimize the rare earth elements leaching from Moroccan phosphogypsum using a nitric acid solution. The Plackett–Burman statistical design was used to identify the statistically significant factors responsible for the optimum leaching conditions. With this purpose, the following seven variables were studied: nitric acid concentration (X1), solid‐to‐liquid ratio (X2), temperature (X3), leaching time (X4), stirring speed (X5), drying (X6), and particle size (X7). Given that the leaching recovery of rare earth elements is limited by the quantity of dissolved phosphogypsum, we examined two simultaneous responses, namely, the leaching efficiency of rare earth elements YREEs and the leaching efficiency of calcium YCa (dissolution rate of phosphogypsum). The predicted values of the two fitted models were in good agreement with the experimental values by a coefficient of determination (R2) equal to 98.6% and 96.50%, respectively. In the model of YREEs, only the effect of drying was found to be statistically insignificant with a p‐value greater than 0.05. Nitric acid concentration, solid‐to‐liquid ratio, and temperature are the only variables having a statistically significant effect in the model of YCa. At a dissolution rate of phosphogypsum equal to 30.13%, the leaching efficiency of rare earth elements from our sample has reached a maximum of 87.55%. The optimal experimental conditions are a nitric acid concentration of 3.3 M, a solid‐to‐liquid ratio of 1/9, a temperature of 75°C, a leaching time of 20 min, a stirring speed of 200 rpm, and d ≤ 100 µm as a particle size.

Behavior of Surface-Active Substances in a Nitric Acid Medium and Prospects for Using Them in Hydrometallurgy

The behavior of surface-active substances (surfactants) is studied using the examples of lignosulfonate (LS) and sodium dodecyl sulfate (SDS) in aqueous and nitric acid media as promising additives for the nitric acid leaching of refractory ore concentrates. The effect the temperature (15–70°С) and concentrations of the surfactant (Csurfactant = 0.02–200 g/dm3) and nitric acid (CHNO3 = 0.1–10 g/dm3) have on the surface tension, critical concentration of micelles (CMC), electrical conductivity, pH, and optical density of solutions is established. The critical association of concentration is determined for lignosulfonate: CLS ~ 0.13–0.14 mol/dm3. An increase in the surface activity of lignosulfonate is noted upon raising the temperature of and adding nitric acid to an LS–H2O system. The established effects (a drop in σl–g) are explained by an increase in the coefficient of diffusion of LS macromolecules and a change in the intensity of the associative-dissociative processes of counterions and the LS polyanion. The positive effect nitric acid has on the surface activity of SDS is noted and found to reduce surface tension at the liquid–gas interface and CMCs. Associative processes in SDS–HNO3 systems are also confirmed by measuring the optical density of the considered systems.

Kinetics of nitric acid leaching of bornite and chalcopyrite

The paper presents a study of the process of nitric acid dissolution of the natural minerals chalcopyrite and bornite. The influence of various parameters, including temperature, nitric acid concentration and particle sizes, on this process was examined. Based on the data obtained, the values of apparent activation energy (57.41 and 42.98 kJ/mol for chalcopyrite and bornite, respectively), empirical orders with respect to nitric acid (1.62 and 1.57 for chalcopyrite and bornite, respectively) and with respect to particle size (–1.16 and –2.53 for chalcopyrite and bornite, respectively) were calculated using the shrinking core model. Generalized kinetic equations for the dissolution process of both minerals were derived. Based on the calculations performed, it was suggested that the dissolution processes of chalcopyrite and bornite under these conditions are limited by internal diffusion.

Neodymium upgrading of tin slag using acid leaching and multistage precipitation

Tin metal production in Indonesia increased in 2018 and 2019. As the production of tin metal increases, the production of slag from tin smelting also increases. Tin slag can be further utilized by extracting valuable metals from it, such as rare earth elements (REE). One of the rare earth elements observed in this study is neodymium (Nd). The use of Nd includes the manufacture of Nd-based permanent magnets. According to individual REE oxide demand and production data in the world, the supply of Nd2O3 in the world is experiencing a shortage of 2,025 tons per year. The purpose of this study is to determine the optimal concentration and ratio of solids to nitric acid in tin slag leaching after the alkaline fusion process and the pH of Nd precipitation. Alkaline fusion as a pre-treatment step to open the silica structure in the slag fusion was carried out for 2 h at 700 °Cwith a ratio of NaOH: slag (gram: gram) = 2:1 to produce frit, which will be leached using water. The residue from water leaching was followed by nitric acid leaching with a concentration variation of 1.75 M, 2.25 M, 2.75 M, 3.25 M, and 3.75 M, then continued with a solid percentage variation of 8%, 11%, 15%, 20%, and 26%. The nitric acid leaching filtrate was precipitated with ammonia at pH 6, 8, and 10. The results obtained were a percent of Nd extraction of 65.172% obtained at a concentration of 3.25 M, a solid percent ratio of 15% with a temperature of 60 °C, a grain size of −200 + 325 mesh, a stirring speed of 250 rpm, and a leaching time of 60 min. Nd deposition efficiency occurred at a pH 6 of 47.79%. Increased Nd content from 1.036% to 3.257%.

A unique sustainable chemical method for the recovery of pure silicon from waste crystalline silicon solar panels

The present work suggests a unique approach for recovering pure silicon from end-of-life silicon solar panels by a direct treatment which does not involve the use of Hydrofluoric Acid (HF). Firstly, the better alkaline treatment between NaOH and KOH was determined. Then, effects of HF etching time and concentration were studied by comparing different etching treatments. Metal impurities such as Ag, Sn, and heavy metal Pb decreased considerably during the acid leaching studies with suitable concentrations. The major impurity Aluminium was reduced significantly by a two-step chemical treatment which ensures minimal silicon loss. Although it is possible to recover 4 N pure silicon by both (with and without HF etching) methods, direct treatment is preferred since the process eliminates potential human health and environmental concerns associated with HF. The recovered silicon samples were analysed by ICP-OES to detect impurity concentration, by XRD for phase identification and SEM analysis for surface morphology. The critical doping impurities, boron and phosphorous dropped considerably to 18.7 ppm and ND in direct treatment. Thus, the study not only provides an alternative way for recovering pure silicon without the use of harmful chemicals such as HF, but it also recommends a 6 M nitric acid leaching treatment before the etching procedure to lower the concentration of metallic impurities. The results are based on treatments with commercial grade chemicals which ensures the scalability of the process at commercial batch. The profit analysis of the recoverable metals was carried out and estimated to be nearly $19 for an 18 kg c-Si module.

Preliminary Flowsheet Development for Mixed Rare Earth Elements Production from Apatite Leaching Aqueous Solution Using Biosorption and Precipitation

A flowsheet was developed to extract mixed Rare Earth Elements (REEs) from an aqueous solution generated by nitric acid leaching of apatite concentrate. In this study, Platanus orientalis (P. orientalis) leaf powder was employed in the biosorption process to purify the pregnant leach solution. The sorption and desorption processes were investigated and optimized. The results demonstrated the successful extraction of REEs from the pregnant leach solution using the biosorbent. Hydrochloric acid effectively desorbed REEs from the loaded P. orientalis leaf powder. Thermodynamic studies indicated that REEs’ sorption on P. orientalis leaf powder was an endothermic and spontaneous process. Precipitation and calcination steps yielded mixed rare earth oxides (REOs) with an assay of approximately 87%. The final product, mixed REOs, can be further refined through releaching and a secondary impurity removal stage prior to entering the individual REE separation process. Alternatively, it can be fed directly into the solvent extraction process or alternative technologies to obtain individual heavy and light REEs.

Development of a Two-Stage Hydrometallurgical Process for Gold-Antimony Concentrate Treatment from the Olimpiadinskoe Deposit.

An integrated two-stage metallurgical process has been developed to process concentrates from the Olimpiadinskoe deposit, which contain high levels of antimony and arsenic. The optimal parameters for the alkaline sulfide leaching process of the initial concentrate from the Olimpiadinskoe deposit were determined to achieve the maximum extraction of antimony at a 99% level. The recommended parameters include an L:S ratio of 4.5:1, a sodium sulfide concentration of 61 g/L, a sodium hydroxide concentration of 16.5 g/L, a duration of 3 h, and a temperature of 50 °C. A synergistic effect of co-processing alkaline sulfide leach cakes with sulfuric and nitric acids was observed. The pre-treatment step reduced the nitric acid composition by converting carbonates into gypsum and increased the arsenic extraction by 15% during subsequent nitric acid leaching. The laboratory research on the nitric acid leaching of decarbonized cake established the key parameters for the maximum iron and arsenic extraction in solution (92% and 98%, respectively), including an L:S ratio of 9:1, a nitric acid concentration of 6 mol/L, and a time of 90 min. Full polynomial equations for the iron and arsenic extraction from the decarbonized cake were derived. The model demonstrated a high relevance, as evidenced by the determination coefficients (R2) of 96.7% for iron and 93.2% for arsenic. The technology also achieved a high gold recovery rate of 95% from the two-stage alkaline sulfide and nitric acid leach cake. Furthermore, the maximum deposition of arsenic from the nitrate leach solution in the form of insoluble As2S3 was determined to be 99.9%. A basic technological flow sheet diagram for processing the flotation gold-antimony concentrate from the Olimpiadinskoe deposit was developed, including two stages: the production of metallic antimony and the gold extraction from the nitric leach cake.

Mass Spectrometry Insight for Assessing the Destiny of Plastics in Seawater

Plastic pollution has become an increasingly serious environmental issue that requires using reliable analytical tools to unravel the transformations of primary plastics exposed to the marine environment. Here, we evaluated the performance of the isotope ratio mass spectrometry (IRMS) technique for identifying the origin of polymer material contaminating seawater and monitoring the compositional alterations due to its chemical degradation. Of twenty-six plastic specimens available as consumer products or collected from the Mediterranean Sea, five plastics were shown to originate from biobased polymeric materials. Natural abundance carbon and hydrogen isotope measurements revealed that biopolymers incline to substantial chemical transformation upon a prolonged exposure to seawater and sunlight irradiation. To assess the seawater-mediated aging that leads to the release of micro/nano fragments from plastic products, we propose to use microfiltration. Using this non-destructive separation technique as a front end to IRMS, the fragmentation of plastics (at the level of up to 0.5% of the total mass for plant-derived polymers) was recorded after a 3-month exposure and the rate and extent of disintegration were found to be substantially different for the different classes of polymers. Another potential impact of plastics on the environment is that toxic metals are adsorbed on their surface from the seashore water. We addressed this issue by using inductively coupled mass spectrometry after nitric acid leaching and found that several metals occur in the range of 0.1-90 µg per g on naturally aged plastics and accumulate at even higher levels (up to 10 mg g-1) on pristine plastics laboratory-aged in contaminated seawater. This study measured the degradation degree of different polymer types in seawater, filling in the gaps in our knowledge about plastic pollution and providing a useful methodology and important reference data for future research.

Waste Treatment and Resource Utilization: Removal and recovery of soluble impurities from nitric acid leaching residue of phosphate rock by electrokinetic

Electrodynamic cleaning techniques for removing and recycling soluble impurities (phosphorus, fluorine, Sr, Pb, Cr, Cu, and Mn) in nitric acid leaching residues of phosphate rock (NG) were investigated. The PO43− concentration of the anode chamber was increased to 207.94 mg/L, while the F− concentration of the cathode chamber rose to 28.33 mg/L. Besides, the soluble phosphorus levels in the cathode regions (R1 and R2) were decreased by 98.02% and 90.16%, respectively. Moreover, the dissolved heavy metals, namely Mn, Cr, Cu and Pb in NG were enriched in the anode chamber, and Sr was enriched in the cathode chamber. The synergistic effects of electrocoagulation and electrodeposition lowered the levels of phosphate, fluoride, and heavy metals in the cathode, thus reducing the decreasing electrical conductivity. The migration and accumulation behaviors of soluble impurities in an electric field were regulated by electromigration, electro-osmotic flow, and electrolysis reaction. Considering that, this paper provides support for the harmless treatment of NG and the recovery of valuable elements, which is conducive to developing the wet-process phosphoric acid process and reducing the large-scale storage of phosphogypsum.