Phase Contact Time Research Articles

EXTRACTION AND CONCENTRATION OF RHENIUM FROM NITRATE-CONTAINING RHENIUM DESORBATE

Extraction technology plays a key role in the industrial production of rhenium, accounting for more than 70% of the world's production of this element. In aqueous and alkaline solutions, rhenium is present in the form of the anion ReO4 - , which necessitates the use of anion exchange extractants based on tertiary amines. Despite the widespread application and many years of research on rhenium extraction with amines, the obtained data remain contradictory. The extraction of rhenium from aqueous solutions by an amine extractant occurs through an anion exchange mechanism with the formation of the complex TAAHReO4. To increase the solubility of amine salts in the organic phase, high-molecular-weight aliphatic alcohols, such as decyl alcohol, are added, which act as modifiers of the organic phase without extracting rhenium themselves. The aim of this work is to investigate the extraction of rhenium with trialkylamine from a model solution that simulates the composition of nitrate desorbate obtained from the processing of uranium ores. Specifically, various factors affecting the extraction and reextraction of rhenium are studied to determine the optimal parameters of these processes. The study uses trialkylamine as the extractant and decyl alcohol as the modifying additive. The results of the study show that the optimal parameters for rhenium extraction are: an extractant concentration of TAA:DA:kerosene=40:5:55 (% by volume), an organic to aqueous phase ratio of V_org/aq = 1:5, an extraction time of 5 minutes, and a rhenium extraction rate of up to 75%. Similar results were obtained with an extractant concentration of TAA:DA:kerosene = 30:10:60 and an extraction time of 5 minutes, where the rhenium extraction rate was about 74%. The re-extraction of rhenium is most efficiently carried out using an ammonia solution with a concentration of 114 g/L NH3⋅H2O and a phase contact time of 10 minutes, with a re-extraction rate of 85.5%. Similar results were obtained with the addition of 174 g/L (NH4)2SO4, where the rhenium re-extraction rate was 82%.

Evaluation of Adsorption Ability of Lewatit® VP OC 1065 and Diaion™ CR20 Ion Exchangers for Heavy Metals with Particular Consideration of Palladium(II) and Copper(II).

The adsorption capacities of ion exchangers with the primary amine (Lewatit® VP OC 1065) and polyamine (Diaion™ CR20) functional groups relative to Pd(II) and Cu(II) ions were tested in a batch system, taking into account the influence of the acid concentration (HCl: 0.1-6 mol/L; HCl-HNO3: 0.9-0.1 mol/L HCl-0.1-0.9 mol/L HNO3), phase contact time (1-240 min), initial concentration (10-1000 mg/L), agitation speed (120-180 rpm), bead size (0.385-1.2 mm), and temperature (293-333 K), as well as in a column system where the variable operating parameters were HCl and HNO3 concentrations. There were used the pseudo-first order, pseudo-second order, and intraparticle diffusion models to describe the kinetic studies and the Langmuir and Freundlich isotherm models to describe the equilibrium data to obtain better knowledge about the adsorption mechanism. The physicochemical properties of the ion exchangers were characterized by the nitrogen adsorption/desorption analyses, CHNS analysis, Fourier transform infrared spectroscopy, the sieve analysis, and points of zero charge measurements. As it was found, Lewatit® VP OC 1065 exhibited a better ability to remove Pd(II) than Diaion™ CR20, and the adsorption ability series for heavy metals was as follows: Pd(II) >> Zn(II) ≈ Ni(II) >> Cu(II). The optimal experimental conditions for Pd(II) sorption were 0.1 mol/L HCl, agitation speed 180 rpm, temperature 293 K, and bead size fraction 0.43 mm ≤ f3 < 0.6 mm for Diaion™ CR20 and 0.315-1.25 mm for Lewatit® VP OC 1065. The maximum adsorption capacities were 289.68 mg/g for Lewatit® VP OC 1065 and 208.20 mg/g for Diaion™ CR20. The greatest adsorption ability of Lewatit® VP OC 1065 for Pd(II) was also demonstrated in the column studies. The working ion exchange in the 0.1 mol/L HCl system was 0.1050 g/mL, much higher compared to Diaion™ CR20 (0.0545 g/mL). The best desorption yields of %D1 = 23.77% for Diaion™ CR20 and 33.57% for Lewatit® VP OC 1065 were obtained using the 2 mol/L NH3·H2O solution.

Extraction and Separation of zirconium using Aliquat 336 from Egyptian black sand

A solvent extraction method has been employed to extract and separate zirconium from the nitric acid medium using 6% tri-caprylmethylammonium chloride (Aliquat 336) [CH3(CH2)7]3N+(CH3) Cl- dissolved in kerosene as diluent. The relevant factors controlling the extraction process of zirconium using Aliquat 336 were studied. These factors include Aliquat 336 concentration, A:O phase ratio, contact time and diluent type. More than 99.6% of Zr was extracted by 6% Aliquat 336 at contact time 10 minutes, phase ratio O:A (v: v) 2:1 and the diluent were kerosene. Third phase formation was studied and dissolving it by using decanol as modifier was also done. Stripping of zirconium from loaded Aliquat 336 has been carried out using 4M H2SO4 as an effective stripping agent. The feasibility of using Aliquat 336 for separation of zirconium was assisted by stripping studies. The loaded zirconium onto Aliquat 336 has been stripped by stripping efficiency 94.18% when using 4M H2SO4 as an efficient eluting agent at 10 minutes contact time and phase ratio O:A (v: v) 1:1.

Sustainable and efficient recovery of lithium from rubidium raffinate via solvent extraction

In recent years, with the increasing prevalence of rechargeable lithium-ion batteries in the burgeoning markets of electric vehicles and portable electronic devices, the consumption of lithium batteries has significantly surged. Hence, the efficient development and utilization of associated lithium resources bear paramount significance. This study aims to recover lithium from rubidium raffinate via solvent extraction. A systematic investigation was conducted to examine the effects of various parameters such as organic phase concentration, contact time, and phase ratio (O/A) during the separation process. The results indicated that the organic phase composed of 0.1 mol/L 4,4,4-Trifluoro-1-phenyl-1,3-butanedione (HBTA) and 0.1 mol/L Trioctylphosphine oxide (TOPO) could efficiently extract lithium from the rubidium raffinate. The optimal conditions were observed at a temperature of 20℃, O/A=1, and a contact time of 5 min. After three-stage countercurrent extraction, a lithium extraction rate of 99.24 % could be achieved, with over 95 % of the sodium easily scrubbed by 0.1 mol/L HCl at an O/A=10. With the use of 3 mol/L HCl, stripping efficiency exceeding 99 % could be attained at an O/A=10, consequently a successful preparation of battery-grade lithium carbonate product was achieved. Regeneration experiments confirmed the organic phase's excellent reproducibility efficiency. Slope analysis and density function theory (DFT) simulations indicated that optimal lithium extraction is achieved when HBTA and TOPO are at equal molar concentrations. The proposed process is expected to provide a green and sustainable route for the recovery of associated lithium resources.

Synthesis and study of the sorption potential of hydrotalcite modified biochars (LDH@BC) with respect to cerium(III) ions

The innovative LDH@BC composites containing combination of metals: Zn/Al, Co/Al, Mg/Al, Ca/Al at the molar ratio 3/1 were synthesized using the co-precipitation method at constant pH. The composites were applied to remove Ce(III) ions from aqueous solutions. Batch experiments were conducted for determination of influence of solution pH, phase contact time, solution concentration and temperature. The kinetic and isotherm parameters were found using the non-linear regression method. As follows from the thermodynamic tests LDH@BC are more effective removal of Ce(III) ions at higher temperature and the sorption process is unforced and spontaneous. The leaching studies proved that 1 mol/L nitric acid is the best desorbing agent for Ce(III) ions deposited on the sorbent surface. Additionally, the composites were investigated applying the XRD and BET analyses (before sorption) as well as the ATR-FTIR, SEM-EDX, XPS methods (before and after the Ce(III) ions sorption). In summary, the introduction of hydrotalcite composed of Zn/Al, Co/Al, Mg/Al, Ca/Al as modifiers of biochar surface produced a potentially more cost-effective, and non-toxic cerium adsorbent for waters and wastewaters treatment.

Impregnated Polymeric Sorbent for the Removal of Noble Metal Ions from Model Chloride Solutions and the RAM Module.

Nowadays, there is a need for new sources of noble metals due to their dwindling natural resources. This paper presents studies on the sorption of noble metals such as Au(III), Pt(IV), Pd(II) and Rh(III) from model chloride solutions on a newly prepared Amberlite XAD-16-Aliquat 336 sorbent. A "warm impregnation" method without the use of toxic organic solvents was applied to impregnate the polymer matrix. The influence of such factors as hydrochloric acid concentration, sorbent mass and phase contact time was investigated. Kinetic as well as adsorption isotherm studies were carried out. The sorption capacity of the synthesized sorbent was Au(III)-94.34 mg/g, Pt(IV)-45.35 mg/g and Pd(II)-46.03 mg/g. Based on thermodynamic considerations, their sorption proved to be endothermic, as the values of ΔH° > 0. Sorption was spontaneous and favourable (ΔG° < 0). After leaching the RAM module, there was obtained a real solution, in which the metal contents were determined: 38.10 mg/g of gold and 1.76 mg/g of palladium. Totals of 99.9% of gold and 45.4% of palladium were removed from the real leaching solution, with other elements in the solution.

Designing of functional zirconium silicates for vanadium ions recovery from model and real wastewaters

The efficient removal of vanadium(V) from model and real wastewaters by using adsorption is challenging due to the different oxidation states of this element. To address this problem, three adsorbents with different functionalities – ZrO2, ZrO2–SiO2, and ZrO2–SiO2–NH2 – were prepared via in situ sol-gel synthesis. To optimize the adsorption process conditions, different pH values, adsorbate concentration, adsorbent mass, temperature, and phase contact time, were evaluated, and the results of static experiments were presented. Furthermore, to describe the process in detail, commonly known kinetic, equilibrium as well intraparticle diffusion models were applied and analyzed. A kinetic study showed that V(V) removal occurred quickly and reached a level higher than 90% within 30 min when ZrO2–SiO2–NH2 was used. What is more, it was demonstrated that the ZrO2–SiO2–NH2 adsorbent exhibited the best properties and capacity in V(V) sorption, with maximum sorption (89.31 mg/g) achieved at optimum process conditions. The prepared adsorbents were thoroughly evaluated in terms of chemical composition, surface nature, morphology and structural properties. The incorporation of vanadium ions into the surface of ZrO2–SiO2–NH2 was proved and the mechanism of adsorption was proposed. The obtained results provided the high potential of the synthesized zirconium silicates in the uptake of vanadium ions from model and real wastewaters, and may open up new possibilities for the design of effective wastewater treatment methods.

Kinetic and Thermodynamic Studies of Precious Metals Sorption on Impregnated Lewatit VP OC 1026 from Chloride Solutions.

Precious metals are used in many branches of industries. Due to their rarity and diminishing natural resources, more and more new methods are being sought to recover them from secondary sources, which can be electronic waste or spent car exhaust converters. This paper presents the research on the recovery of precious metals from chloride solutions using the Aliquat 336-impregnated Lewatit VP OC 1026 sorbent. The study used a warm impregnation method without toxic solvents, which is beneficial for the environment. The maximal sorption capacities obtained for model solutions in 0.1 M HCl were: 95.6 mg/g for gold, 38.2 mg/g for palladium, and 36.2 mg/g for platinum. There were studied: kinetics and thermodynamics of sorption, as well as amounts of the sorbent, effects of phase contact time and HCl concentration on the sorption of precious metals. Positive values of enthalpy change ΔH° validate that the process is endothermic. The research was also carried out on a real leaching solution obtained by digesting a spent catalytic converter, containing small amounts of platinum group metals. Desorption of precious metal ions was conducted using 1 M thiourea in 1 M hydrochloric acid. The obtained impregnated sorbent proved to be effective for sorption of Au(III), Pd(II), Pt(IV) ions.

Improved Soil Amendment by Integrating Metal Complexes and Biodegradable Complexing Agents in Superabsorbents.

The superabsorbents' application as materials for the preparation of modern mineral fertilizers of controlled activity is presented. Under the static conditions, the commercial acrylic-based Agro® Hydrogel was used as a sorbent for Cu(II), Fe(III), Mn(II), and Zn(II) ions in the presence of three biodegradable complexing agents of the new generation: (N-1,2-dicarboxyethyl)-D,L-aspartate acid (IDHA), N,N-ethylenediaminedisuccinic acid (EDDS) and N,N-bis(carboxymethyl) glutamic acid (GLDA). The ions and complexes concentrations were determined by the inductively coupled plasma optical emission spectrometer (ICP-OES). The characterization of hydrogel before and after the adsorption process was made using the Fourier transform infrared spectroscopy (FT-IR), surface area determination (ASAP), scanning electron microscopy (SEM-EDS) as well as the thermogravimetric (TGA) methods. The influence of the phase contact time, initial concentration, and pH on the adsorption capacities was investigated. The kinetic and adsorption parameters were determined. The Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin adsorption models were applied to describe the experimental data. The Langmuir isotherm model accurately characterized the equilibrium process. The adsorption process was fast, and it reached equilibrium after 60 min of the phase contact time. The research on the adsorption of Cu(II), Fe(III), Mn(II), and Zn(II) onto Agro® Hydrogel with IDHA, EDDS, and GLDA indicates that these complexing agents improve process efficiency.

GLDA and ion exchangers: Unlocking sustainable solutions for recovery of rare earth elements

GLDA (tetrasodium salt of N,N-bis(carboxymethyl)-L-glutamic acid) was proposed as a complexing agent for rare earth elements. The formed complexes Ln(III)-GLDA were subjected to adsorption using twelve commercial ion exchangers of different types. Ion exchangers were characterized by describing their physicochemical properties using sieve analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The stability constants of the Ln(III)-GLDA complexes in the binary systems at different Ln(III):GLDA molar ratios were determined by the potentiometric method. The effects of different process parameters (Ln(III):GLDA molar ratio, initial solution pH, phase contact time, initial solution concentrations, and temperature) on the adsorption of La(III), Nd(III), and Ho(III) ions in the presence of GLDA were investigated by the static method in the single-component systems.Kinetic, equilibrium, and thermodynamic parameters were calculated. The highest adsorption capacities were obtained for the Purolite S957 ion exchanger (139.57 mg/g for the La(III)-GLDA complexes, 152.72 mg/g for the Nd(III)-GLDA complexes, and 151.29 mg/g for the Ho(III)-GLDA complexes), Lewatit Monoplus SP112 ion exchanger (155.49 mg/g for the La(III)-GLDA complexes, 150.23 mg/g for the Nd(III)-GLDA complexes, and 132.77 mg/g for the Ho(III)-GLDA complexes). The desorption process was performed to regenerate the ion exchangers by applying hydrochloric and nitric(V) acids at concentrations of 0.5, 1, and 2 M. In addition, for La(III)-GLDA complexes, experiments were performed in the column systems.

Production of Mineral-Carbon Composites and Activated Carbons as a Method of Used Gear Oil, Ashes, and Low-Quality Brown Coals Management.

The main objective of this study was to assess the usefulness of the low-quality brown coal, ash obtained as a result of its combustion, as well as used gear oil for the production of mineral-carbon adsorbents. The adsorbents were characterized in terms of textural parameters, acidic-basic character of the surface, mineral matter contribution to the structure, as well as their suitability for drinking water purification. Adsorption tests were carried out against two synthetic dyes-methylene blue and methyl orange. In order to understand the nature of the organic pollutants adsorption, the effect of the initial dye concentration, temperature, and pH of the system as well as the phase contact time were investigated. The obtained mineral-carbon composite and activated carbons significantly differed not only in terms of the elemental composition and chemical character of the surface (from slightly acidic to strongly alkaline), but also showed a very diverse degree of specific surface development (from 21 to 656 m2/g) and the type of porous structure generated (from micro/mesoporous to typically mesoporous). Adsorption tests showed that the efficiency of organic dye removal from aqueous solutions primarily depends on the type of the adsorbent and adsorbate applied, and, to a lesser extent, on the temperature and pH of the system. In turn, kinetic studies have shown that the sorption of dyes on such materials is consistent with a pseudo-second-order kinetics model, regardless of the type of adsorbed dye.

Cyclic utilization of waste aluminum polishing solution by an efficient co-extraction system: Influence factors and extraction mechanism

For the purpose of regenerating waste aluminum polishing solution and eliminating its potential threats to environmental safety, this work focuses on establishing a highly effective co-extraction system for the simultaneous recovery of H3PO4 and H2SO4 from this kind of hazardous wastes, and further reveals the main influence factors and extraction mechanisms. Through a series of screening experiments, a co-extraction system including tributyl phosphate and 1-butanol was successfully established, and the experimental results verified the suitability of this system for the regeneration of most H3PO4 and H2SO4 from waste aluminum polishing solution. The McCabe-Thiele diagram was used to determine that the whole extraction process was a counter-current process of 4-stage extraction and 2-stage stripping, which was capable of recovering most of H3PO4 and H2SO4. The main influence factors include phase ratio, temperature, and contact time, which have different degrees of influence on the recovery efficiency. The co-extraction mechanism of H3PO4 and H2SO4 has also been confirmed by the methods of FTIR, 1H NMR, 17O NMR and 31P NMR.

Preconcentration of Zinc, Cadmium, and Mercury(II) Ions on a Polymeric Modified Adsorbent Based on a Highly Basic ARA-8p Anionite and a Rhodanine Derivative

We studied the conditions for the adsorption of zinc, cadmium, and mercury(II) ions on a modified adsorbent based on an ARA-8p highly basic anion exchange resin and a Rhodanine derivative, 5-(4-carboxyphenyl-azo)rhodanine (ARA-8p-p-KBAR), in a batch mode. The values of pH, phase contact time, and adsorbate concentration at which the maximum recovery of zinc, cadmium, and mercury(II) ions was achieved were determined. The adsorption capacity of the adsorbent for the adsorbed ions was determined from the obtained adsorption isotherms. The calculated value of the free energy shows that adsorption proceeds with the formation of an ionic bond. Eluents were selected to ensure the quantitative desorption of zinc, cadmium, and mercury(II) ions. The interfering effect of macrocomponents and trace elements of water was studied; zinc, cadmium, and mercury(II) ions were quantitatively adsorbed by this adsorbent from a solution of a complex composition. A procedure was developed for the adsorption–atomic-absorption determination of zinc, cadmium, and mercury(II) ions in various water samples.

Used Filter Cartridges as Potential Adsorbents of Organic Pollutants

The main objective of this study was to assess the usefulness of exhausted activated carbon-based filter cartridges for the removal of organic pollutants from aqueous solutions using the example of two model pollutants: synthetic dyes with different particle sizes, i.e., methylene blue (MB) and malachite green (MG). In order to determine the organic dyes’ adsorption mechanism, the effects of phase contact time, initial dye concentration, pH, and temperature of the system were investigated. Langmuir and Freundlich isotherm models were employed to analyze the experimental data. Additionally, all adsorbents were characterized in terms of the ash content, type of porous structure, presence of surface functional groups, pH value, and iodine adsorption number—which is one of the quality control parameters of activated carbons. Adsorption tests have shown that carbonaceous materials from bottle filters and filter jugs can be successfully used for the removal of organic dyes from the liquid phase. The maximum sorption capacity of this type of adsorbent towards methylene blue was 333.06 mg/g, while in the case of malachite green it was 308.75 mg/g. For all carbonaceous materials, a better fit to the experimental data was achieved with a Langmuir isotherm than a Freundlich one. It has also been shown that the efficiency of MB and MG adsorption from aqueous solutions decreases with increasing temperature of the system—the best results were obtained at 25 °C. A better fit of the kinetics data was achieved using the pseudo-second order model.

Green Extractants in Assisting Recovery of REEs: A Case Study.

The recycling of REEs from the end of life (EoL) products, such as nickel metal hydride batteries (NiMH), offers great opportunities for their supply in Europe. In the presented paper, the application of 'green' extractants such as citric (CA), metatartaric (TA), and ethylenediaminedisuccinic acid (EDDS) (also with H2O2 addition) for the recovery of REEs was studied. The studies were conducted considering the effects of the phase contact time, the initial concentration of CA, TA, and EDDS, as well as H2O2, pH, and temperature. It was found that the addition of TA to the CA solution meant that higher rates of metal ion binding and, thus, leaching was observed. The optimal conditions were obtained in the system: CA-TA and H2O2 for the concentration 0.6M-0.3 M-2%.

A green hybrid extraction process for thiophene, quinoline and indole recovery from light hydrocarbon fractions

"Green" extraction technologies are fundamental to many processing plants in order to improve the deteriorating environmental situation in the world. This work presents a combination of two "green" extraction technologies: liquid extraction based on water-soluble polymers, as an environmentally attractive method for the isolation, separation and concentration of substances, and supercritical fluid extraction, as an environmentally safe method for the isolation of valuable components from aqueous polymer solutions. Polyvinylpyrrolydone 3500 (PVP-3500) has demonstrated high extraction ability for quinoline and indole with one-step extraction efficiency up to 82% and 94% respectively from solutions simulating light hydrocarbon fractions. Concomitant versatile research allowed building the dependences between quantitative quinoline and indole extraction characteristics and such process parameters as: the phases contact time, the extraction system composition, the initial concentration of nitrogen-containing compounds in n-hexane, the volume fraction of the extractant and the process temperature in the heterogeneous system PVP-3500 – n-hexane – water. It was found that PVP-3500 possesses weak extraction affinity for sulfur-containing compounds, which makes it promising for use in the separation of S- and N-containing heterocyclic compounds. In addition, we propose a new environmentally friendly approach for the purification of polymers used in the study based on the countercurrent extraction with supercritical carbon dioxide. Particularly, using the latter method instead of static supercritical purification mode leads to significant increase in quinoline and indole extraction efficiency from an aqueous solution of PVP-3500.

Determination of the Ni(II) Ions Sorption Mechanism on Dowex PSR2 and Dowex PSR3 Ion Exchangers Based on Spectroscopic Studies.

This paper estimates the suitability of the strongly basic anion exchangers, Dowex PSR2 and Dowex PSR3, as sorbents of nickel ions in aqueous solutions. These actions are aimed at searching for new solutions due to the growing discharge of nickel into wastewaters, primarily due to its addition to steel. The nickel sorption experiments were conducted under static conditions and resulted in the optimization of pH, phase contact time, initial solution concentration, and temperature. The next step was to calculate the kinetic, isothermal, and thermodynamic parameters. Moreover, the ion exchangers were characterized by means of Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and CHN elemental analysis. It was found that the sorption process was most effective at pH 6 after 240 min and at the temperature of 293 K. The values of the thermodynamic parameters revealed that the adsorption was exothermic and spontaneous. The physicochemical analyses combined with the experimental research enabled determination of the sorption mechanism of Ni(II) ions.

Imidazolium-Modified Silica Gel for Highly Selective Preconcentration of Ag(I) from the Nitric Acid Medium

The ion-exchange behavior of an organomineral material with an imidazolium (1-methyl-3-(prop-2-yn-1-yl)-1H-imidazol-3-ium bromide)-modified silica gel was studied for the extraction of Ag(I) from nitric acid media. The extraction from multicomponent systems containing Fe(III), Co(II), Ni(II), Cu(II), Pb(II), and Mn(II) in 100- and 1000-fold molar excesses with respect to Ag(I) was shown to occur with high selectivity. Based on the data of X-ray diffraction and X-ray fluorescence spectroscopy for samples of modified silica gel, a mixed ion exchange–adsorption mechanism for the extraction of Ag(I) was proposed. The effect of the phase contact time and the concentration of nitric acid on the distribution coefficient of Ag(I) was studied. The selectivity factors of the extraction of Ag(I) from multicomponent systems containing foreign cations in 100- and 1000-fold molar excesses under steady-state and dynamic concentration conditions were calculated.

APPLICATION OF RICE PAD (ORYZA SATIVA) AS A SORPTION MATERIAL TO REMOVE POLLUTANTS FROM AQUATIC ENVIRONMENT

The use of rice husk (the waste in the production of seeded rice (Oryza sativa) as a sorption material for the removal of pollutants of various classes – inorganic (Cr, Ni, Co, Pb, Hg, As, Cd, Cu, Zn) and organic substances (synthetic and natural dyes, phenols, antibiotics, polycyclic aromatic compounds, humic acids, pesticides, chitosan) from aqueous media is generalized. The literature data on the structure of seeded rice, the volume of its cultivation, the chemical composition, and some components of rice husk are given.&#x0D; The methods of physical and chemical (the use of inorganic acids, salts, and alkalis) are described activation, as well as modification of rice husks using surfactants, Fe3O4 nanoparticles, functional agents, and monomers (polymerization reactions). Quantitative characteristics of the absorption of various pollutants (recoveries, equilibrium limit sorption) are given. The influence of pH, temperature, the concentration of pollutants, phase contact time, volume, and mass of rice husk on sorption and removal of pollutants from aqueous media is shown. Possible sorption mechanisms, kinetic and sorption models are described. It is revealed that the isotherms of the sorption of pollutants in most cases are most adequately described by Langmuir and Freundlich models, and the kinetics of the process is a pseudo-second-order model.

Chitosan-Modified Biochars to Advance Research on Heavy Metal Ion Removal: Roles, Mechanism and Perspectives.

The chitosan-modified biochars BC-CS 1-1, BC-CS 2-1 and BC-CS 4-1 were subjected to the synthetic application of biochar from agriculture waste and chitosan for the adsorption of Cu(II), Cd(II), Zn(II), Co(II) and Pb(II) ions from aqueous media. The results displayed a heterogeneous, well-developed surface. Additionally, the surface functional groups carboxyl, hydroxyl and phenol, determining the sorption mechanism and confirming the thermal stability of the materials, were present. The sorption evaluation was carried out as a function of the sorbent dose, pH, phase contact time, initial concentration of the solution and temperature. The maximum value of qt for Pb(II)-BC-CS 4-1, 32.23 mg/g (C0 200 mg/L, mass 0.1 g, pH 5, 360 min), was identified. Nitric acid was applied for the sorbent regeneration with a yield of 99.13% for Pb(II)-BC-CS 2-1. The produced sorbents can be used for the decontamination of water by means of the cost-effective and high-performance method.