Study on Adsorption and Aggregation in the Mixed System of Polyacrylamide, Cu(II) Ions and Innovative Carbon–Silica Composite

The paper presents an original study on adsorption and aggregation phenomena in a mixed system consisting of a macromolecular compound, heavy metal ions and an innovative adsorbent. The authors used ionic polyacrylamides (PAM), Cu(II) ions and carbon–silica composite (C-SiO2) in the experiments. Such a system has not yet been described in the literature and therefore, the article is of significant novelty and great importance. The composite was prepared by mixing phenol–formaldehyde resin with silica and pyrolysis at 800 °C. The adsorbed amounts of Cu(II) ions and PAM were determined spectrophotometrically. C-SiO2 was characterized using potentiometric titration, microelecrophoresis and Fourier Transform Infrared Spectroscopy (FTIR) analysis. In turn, the C-SiO2 aggregation was established turbidimetrically as well as using a particle size analyzer. The obtained results indicated that both Cu(II) ions and ionic polyacrylamide were adsorbed on the composite surface at pH 6. The highest noted adsorbed amounts were 9.8 mg/g for Cu(II) and 35.72 mg/g for CT PAM-25%. Cu(II) ions increased the anionic PAM adsorbed and reduced the cationic PAM one. The adsorption of anionic PAM (50 ppm) stimulated the solid aggregation significantly. What is more, Cu(II) ions enhanced this process. The size of particles/aggregates formed without additives equaled 0.44 μm, whereas in the mixed Cu(II)/AN PAM system, they were even at 1.04 μm

The structure of electrical double layer formed on the kaolinite surface in the mixed system of cationic polyacrylamide and lead (II) ions

The bioavailability of toxic heavy metalsfor organisms depends mainly on the soil physicochemical properties, i.e. type and granulometric composition, pH value, redox potential, individual fractions content and microorganisms presence. The addition of artificial fertilizers rich in humic substances or polyacrylamide soil flocculants may also affect the content of easily absorbed heavy metal forms. Due to their chelating properties, the added substances can bind metal ions in the form of complexes characterized by low mobility in soil environment. As a consequence, the immobilization process takes place, which is a desirable phenomenon for organism health.The aim of the study was to determine the structure of electrical double layer formed on the kaolinite surface in the mixed system of cationic polyacrylamide and lead(II) cations. The influence of cationic PAM presence on the Pb(II) ions sorption on the kaolinite surface as well as heavy metal ion addition on the polymer adsorbed amount on the same clay mineral were studied. The adsorption and electrokinetic properties of studied kaolinite/CT PAM/Pb(II) systems were determined based on the spectrophotometric study, zeta potential measurements as well as potentiometric titration

Comparison of Physicochemical Properties of Fly Ash Precursor, Na-P1(C) Zeolite–Carbon Composite and Na-P1 Zeolite—Adsorption Affinity to Divalent Pb and Zn Cations

Considering the growing needs of environmental remediation, new effective solutions should be sought. Therefore, the adsorbed amounts of heavy metal ions, such as lead(II) and zinc(II), on the surface of high-carbon fly ash (HiC FA), zeolite-–carbon composite (Na-P1(C)) and pure zeolite (Na-P1), were investigated. The applied solids were characterized using the following techniques: XRD, SEM-EDS, TEM, porosimetry, SLS, electrophoresis and potentiometric titration. The heavy metal concentration in the probes was determined by applying ICP-OES spectroscopy. Adsorption/desorption and electrokinetic measurements were performed in the systems containing one or two adsorbates. The obtained results indicated that Pb(II) ions are adsorbed in larger amounts on the investigated solid surface due to the molecular sieving effect. The largest adsorption capacity relative to lead(II) ions was observed for pure Na-P1 zeolite (407 mg/g). The simultaneous presence of Pb(II) + Zn(II) mixed adsorbates minimally affects the amount of adsorbed Pb(II) ions and causes a significant decrease of Zn(II) ion adsorption (in comparison with analogous systems containing single adsorbates). It was also shown that all solids can be efficiently regenerated using hydrochloric acid. Thus, the selected pure zeolite can be successfully applied in soil remediation or other purifying technologies as an effective Pb(II) adsorbent

Comparison of Monovalent and Divalent Ions Removal from Aqueous Solutions Using Agricultural Waste Biochars Prepared at Different Temperatures—Experimental and Model Study

Copper (Cu) and silver (Ag) occur naturally in the environment but have toxic effects on organisms at elevated concentrations. This paper discussed the removal of Cu and Ag from aqueous solutions using biochars obtained at different pyrolysis temperatures. Three biomass sources—sunflower husks (SH), a mixture of sunflower husks and rapeseed pomace (SR) and wood waste (WW)—were pyrolyzed at 300, 400 and 500 °C. Biochars produced at 500 °C exhibited a higher specific surface area, lower variable surface charge and lower contents of surface functional groups than those obtained at 400 or 300 °C. The pseudo-second-order model and intra-particle diffusion (IPD) model well-described the Cu and Ag adsorption kinetics. The Cu adsorption was about 1.48 times slower than the Ag adsorption on the biochars obtained at 500 °C. The model of Langmuir-Freundlich well-described the equilibrium adsorption. Agricultural biochars obtained at >500 °C had a surface with a higher affinity to attract Ag than Cu and were able to remove a larger amount of heavy metals from aqueous media than those prepared at lower pyrolysis temperatures

Carboxin and Diuron Adsorption Mechanism on Sunflower Husks Biochar and Goethite in the Single/Mixed Pesticide Solutions

The study focused on the adsorption mechanism of two selected pesticides: carboxin and diuron, on goethite and biochar, which were treated as potential compounds of mixed adsorbent. The authors also prepared a simple mixture of goethite and biochar and performed adsorption measurements on this material. The adsorbents were characterized by several methods, inter alia, nitrogen adsorption/desorption, Boehm titration, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The adsorption study included kinetics and equilibrium measurements, in the solution containing one or two pesticides simultaneously. The adsorption data were fitted to selected theoretical models (e.g., Langmuir, Freudlich, Redlich–Peterson, pseudo first-order and pseudo second-order equations). Based on the obtained results, it was stated that, among all tested adsorbents, biochar had the highest adsorption capacity relative to both carboxin and diuron. It equaled 0.64 and 0.52 mg/g, respectively. Experimental data were best fitted to the pseudo second-order and Redlich–Peterson models. In the mixed systems, the adsorption levels observed on biochar, goethite and their mixture were higher for diuron and lower for carboxin, compared to those noted in the single solutions. The presented results may enable the development of new mixed adsorbent for remediation of soils polluted with pesticides

Purification of Aqueous Media by Biochars: Feedstock Type Effect on Silver Nanoparticles Removal

Due to the harmful effects of nanoparticles in the environment, their effective removal from aqueous media is of great importance. This paper described the research on the silver nanoparticles (Ag-NPs) sorption on biochars obtained from different feedstock types. The sorbents were produced through pyrolysis (double-barrel method) of the vineyard (BV), paulownia tree (BP), and tobacco (BT). BV exhibited the highest specific surface area, porosity, value of variable surface charge, and content of surface acidic functional groups among the used biochars. The pseudo-second order model best described the obtained adsorption kinetics, whereas the Freundlich model accounted for the registered adsorption data. The Ag-NPs removal was highly efficient in the case of BV, especially in the nanoparticle concentration range 50–500 mg/L. Thus, this biochar can be considered as an ecofriendly, effective, low-cost organic adsorbent, potentially used in the aqueous media purification

Simultaneous Removal of Pb2+ and Zn2+ Heavy Metals Using Fly Ash Na-X Zeolite and Its Carbon Na-X(C) Composite

Pure zeolite (Na-X) and a zeolite–carbon composite (Na-X(C)) were investigated as adsorbents of heavy metals—Pb2+ and Zn2+ from an aqueous solution. These materials were synthesized from fly ash—a waste from conventional hard coal combustion. Both solids were characterized using XRD, SEM-EDS, nitrogen adsorption/desorption, particle size and elemental composition analyses. The adsorption study was performed at pH 5 in the systems containing one or two adsorbates simultaneously. The obtained results showed that the pure zeolite was characterized by a more developed surface area (728 m2/g) than its carbon composite (272 m2/g), and the mean pore diameters were equal to 1.73 and 2.56 nm, respectively. The pure Na-X zeolite showed better adsorption properties towards heavy metals than its Na-X(C) composite, and Zn2+ adsorbed amounts were significantly higher than the Pb2+ ones (the highest experimental adsorption levels were: for Zn2+—656 and 600 mg/g, and for Pb2+—575 and 314 mg/g, on the Na-X and Na-X(C) surfaces, respectively). The zinc ions are exchanged with the cations inside the zeolite materials structure more effectively than lead ions with a considerably larger size. In the mixed systems, the competition between both heavy metals for access to the active sites on the adsorbent surface leads to the noticeable reduction in their adsorbed amounts. Moreover, the hydrochloric acid was a better desorbing agent for both heavy metals, especially Pb2+ one (desorption reached 78%), than sodium base (maximal desorption 25%)

Green Synthesis and Efficient Adsorption: Na-X Zeolite vs. C/Mn/SiO₂ Composite for Heavy Metals Removal

The studies aimed to test the adsorption capacity of two silica-enriched porous materials, synthetic Na-X zeolite and Mn-containing carbon composite, towards Pb(II) and Zn(II) ions in single and mixed systems and in the presence of diclofenac (DCF) and (or) poly(acrylic acid) (PAA). The synthetic zeolite was characterized by a well-developed surface area of 728 m2/g and a pore diameter of 1.73 nm, while the carbon composite exhibited 268 m2/g and 7.37 nm, respectively. Na-X was found to be more efficient than the carbon composite (75–212 mg/g) in adsorbing heavy metal ions in both single and bimetallic systems (322–333 mg/g). In turn, the C/Mn/SiO2 composite was more effective in removing Pb(II) ions from the systems that simultaneously contained DCF or PAA (480 and 476 mg/g, respectively). The Na-X zeolite demonstrated the greatest stability in all the systems studied. The highest stability was observed in the DCF + Pb(II) mixture, in contrast to the carbon composites where the stability was much lower. To evaluate the possibility of regeneration of the solids, HCl proved to be the best desorbent for heavy metal ions (efficiency of 99%). In general, both adsorbents offer promising potential for solving environmental problems

Impact of Sinorhizobium meliloti Exopolysaccharide on Adsorption and Aggregation in the Copper(II) Ions/Supporting Electrolyte/Kaolinite System

To obtain insight into physicochemical interactions between Cu(II) ions, kaolinite, and exopolysaccharide (EPS) synthesized by Sinorhizobium meliloti Rm 1021 soil bacteria, an adsorption, electrokinetic, and aggregation study was performed in the selected systems. The obtained data showed that supporting electrolyte type affects both EPS and Cu(II) ions adsorption. For initial Cu(II) concentration 100 mg/L, 4.36 ± 0.25 mg/g (21.80 ± 1.00%) of the ions were adsorbed in 0.001 M NaCl and 3.76 ± 0.20 mg/g (18.80 ± 1.00%) in 0.001 M CaCl2. The experimental data were best fitted to the Langmuir model as well as pseudo second-order equation. The EPS adsorbed amount on kaolinite was higher in the CaCl2 electrolyte than in NaCl one. For an initial polymer concentration of 100 mg/L, the EPS adsorbed amount was 4.69 ± 0.08 mg/g (23.45 ± 0.40%) in 0.001 M NaCl and 5.26 ± 0.15 mg/g (26.32 ± 0.75%) in 0.001 M CaCl2. In the mixed system, regardless of electrolyte type, exopolysaccharide contributed to immobilization of higher amount of copper(II) ions on the clay mineral. Also, in the samples containing heavy metal ions and exopolysaccharide simultaneously, the aggregation of kaolinite particles was the strongest. The results presented in the paper may be very helpful in soil bioremediation, especially in the development of technologies reducing the mobility of heavy metals in the environment