Removal of Pb2+ from aqueous solution by adsorption on chemically modified muskmelon peel

A critical review on the separation of heavy metal(loid)s from the contaminated water using various agricultural wastes

Wastewater contamination with heavy metal(loids)s has become a worldwide environmental and public health problem due to their toxic and non-degradable nature. Different methods and technologies have been applied for water/wastewater treatment to mitigate heavy metal(loid)-induced toxicity threat to humans. Among various treatment methods, adsorption is considered the most attractive method because of its high ability and efficiency to remove contaminants from wastewater. Agricultural waste-based adsorbents have gained great attention because of high efficiency to heavy metal(loids)s removal from contaminated water. Chemically modified biosorbents can significantly enhance the stability and adsorption ability of the sorbents. The two mathematical models of sorption, Freundlich and Langmuir isotherm models, have mostly been studied. In kinetic modeling, pseudo-second-order model proved better in most of the studies compared to pseudo-first-order model. The ion exchange and electrostatic attraction are the main mechanisms for adsorption of heavy metal(loid)s on biosorbents. The regeneration has allowed various biosorbents to be recycled and reused up to 4-5 time. Most effective eluents used for regeneration are dilute acids. For practical perspective, biosorbent removal efficiency has been elucidated using various types of wastewater and economic analysis studies. Economic analysis of adsorption process using agricultural waste-based biosorbents proved this approach cheaper compared to traditional commercial adsorbents, such as chemically activated carbon. The review also highlights key research gaps to advance the scope and application of waste peels for the remediation of heavy metal(loid)s-contaminated wastewater.

Potential Use of Low-Cost Agri-Food Waste as Biosorbents for the Removal of Cd(II), Co(II), Ni(II) and Pb(II) from Aqueous Solutions

We evaluated the potential use of agri-food waste for the removal of heavy metal ions from aqueous solutions and its application in different processes (e.g., water remediation, in the production of biomass enriched in nutritionally significant elements, etc.). Biomasses from grape seed, grape pomace, loquat seed, Calabrese broccoli stem, empty pods of carob and broad bean pods, unripe bitter orange peel, kumquat, orange pulp and Canary Island banana pulp were prepared. The percentages and biosorption capacities were evaluated and compared with those refe-renced using Valencia orange peel (Citrus sinensis Valencia late). These studies allow for easily providing added value to different agri-food wastes. The results show that the proposed biomasses were able to retain the studied metal ions and obtained different percentages, being in some cases above 90%. The highest values were obtained using broad bean pod (Pb(II) (91.5%), Cd(II) (61.7%), Co(II) (40.7%) and Ni(II) (39.7%)). Similar values were observed using grape seed, broccoli stem, carob pod and unripe bitter orange peel. Carob pod for biosorption of Cd(II) is also of great interest. These studies suggest that the agri-food residues evaluated can be applied to prepare effective biosorbents of divalent metal ions from aqueous solutions.

Efficient Removal of Pb(II) from Aqueous Medium Using Chemically Modified Silica Monolith

The adsorptive removal of lead (II) from aqueous medium was carried out by chemically modified silica monolith particles. Porous silica monolith particles were prepared by the sol-gel method and their surface modification was carried out using trimethoxy silyl propyl urea (TSPU) to prepare inorganic–organic hybrid adsorbent. The resultant adsorbent was evaluated for the removal of lead (Pb) from aqueous medium. The effect of pH, adsorbent dose, metal ion concentration and adsorption time was determined. It was found that the optimum conditions for adsorption of lead (Pb) were pH 5, adsorbent dose of 0.4 g/L, Pb(II) ions concentration of 500 mg/L and adsorption time of 1 h. The adsorbent chemically modified SM was characterized by scanning electron microscopy (SEM), BET/BJH and thermo gravimetric analysis (TGA). The percent adsorption of Pb(II) onto chemically modified silica monolith particles was 98%. An isotherm study showed that the adsorption data of Pb(II) onto chemically modified SM was fully fitted with the Freundlich and Langmuir isotherm models. It was found from kinetic study that the adsorption of Pb(II) followed a pseudo second-order model. Moreover, thermodynamic study suggests that the adsorption of Pb(II) is spontaneous and exothermic. The adsorption capacity of chemically modified SM for Pb(II) ions was 792 mg/g which is quite high as compared to the traditional adsorbents. The adsorbent chemically modified SM was regenerated, used again three times for the adsorption of Pb(II) ions and it was found that the adsorption capacity of the regenerated adsorbent was only dropped by 7%. Due to high adsorption capacity chemically modified silica monolith particles could be used as an effective adsorbent for the removal of heavy metals from wastewater.

Ninhydrin-functionalized chitosan for selective removal of Pb(II) ions: Characterization and adsorption performance

A chitosan-based adsorbents (CS-Ninhydrin) was prepared by grafting ninhydrin for Pb(II) ions adsorption. SEM-EDS, XRD and FTIR analysis were used to characterize the synthesized CS-Ninhydrin. The static adsorption experiments showed that CS-Ninhydrin had a good removal rate for Pb(II) ions in a wide range of pH 3 to 7, quickly reached equilibrium (120 min) and had a higher adsorption capacity (196 mg/g). Pseudo second-order and Langmuir models showed that the adsorption process of Pb(II) by CS-Ninhydrin was a single-layer chemical adsorption. Temperature experiments showed that the reaction was a spontaneous exothermic process. In the wastewater experiment, CS-Ninhydrin showed an excellent selectivity to Pb(II) ions. The reusability of CS-Ninhydrin was perfect after five adsorption-desorption cycles. The main adsorption mechanism was the chelating and electrostatic action between N and O groups in CS-Ninhydrin and Pb(II) ions. Therefore, the new adsorbent CS-Ninhydrin was expected to promote the wide application of chitosan in Pb(II) adsorption.

Lead ion adsorption on functionalized sugarcane bagasse prepared by concerted oxidation and deprotonation

Targeting the removal of Pb²⁺ in wastewater, sugarcane bagasse was treated with nitric acid and an alkaline solution to prepare adsorbents. On a typical adsorbent, the adsorption isotherms agreed well with the Langmuir expression, and the maximum adsorption capacity reached 200.3 mg/g. In the presence of 150 ppm Ca²⁺, a common cation in natural water, the Pb²⁺ adsorption capacity slightly declined. In contrast, Mg²⁺ obviously prohibited the adsorption for Pb²⁺. The spent adsorbent could be regenerated at least five times through elution with an EDTA solution. EDS and XPS results demonstrated that nitric acid functioned as an oxidant instead of nitrification agent in the treatment of bagasse. The adsorption process was consistent with quasi-second-order kinetics. Based on thermodynamic studies, the changes in enthalpy and Gibbs free energy were calculated to be - 33.3 and ca. - 18 kJ/mol, indicating that the adsorption process was exothermic and spontaneous. The equilibrium Pb²⁺ adsorption amounts were proportional to the numbers of carboxylate groups on different adsorbents. The binding energies of Pd 4f_5/2 and Pd 4f_7/2 XPS spectra of Pb²⁺ adsorbed were 0.6-0.7 eV lower than those of free Pb(NO₃)₂, indicating the transfer of electrons during adsorption. The conversion of hydroxymethyl groups in sugarcane bagasse into carboxylate groups, as well as the chelation between Pb²⁺ ions and carboxylate groups, was validated in this work, which is beneficial for the treatment of wastewater polluted by lead ions.

Utilización de subproductos agroindustriales para la bioadsorción de metales pesados

La contaminación por metales pesados es un problema que afecta a los ambientes acuáticos y terrestres, y cuya principal fuente son las actividades antrópicas. Para atender este problema, la comunidad científica ha desarrollado métodos físico-químicos para la remoción de metales pesados en efluentes contaminados: sin embargo, la mayoría no son económicamente favorables, ya que presentan elevados costos de operación y mantenimiento, además de que algunos generan residuos difíciles de manejar. Sin embargo, existe un método de bajo costo, altamente eficiente y sin formación de contaminantes secundarios, denominado bioadsorción. La bioadsorción utiliza subproductos agroindustriales con el objetivo de utilizar la excesiva generación de estos residuos como bioadsorbentes, para la remoción de metales pesados en aguas residuales. La utilización de subproductos agroindustriales como bioadsorbentes ha mostrado ser una alternativa para su aprovechamiento, consecuentemente, México tiene potencial en la producción de bioadsorbentes. El objetivo de esta revisión es proporcionar información sistematizada del método de remoción de metales pesados por bioadsorción a través del uso de subproductos agroindustriales.

Dynamic filtration and static adsorption of lead ions in aqueous solution by use of blended polysulfone membranes with nano size MCM-41 particles coated by polyaniline

MCM-41 mesopore was prepared by hydrothermal method and used for synthesis of polyaniline/MCM-41 nanocomposite via in situ polymerization. The nanocomposite was blended with polysulfone to prepare mixed matrix membrane in different content of nanocomposite by phase inversion method. Structural and surface properties of the samples were characterized by SEM, XRD, FTIR, AFM, TGA, BET, and zeta potential measurements. Effect of the nanocomposite content on the hydrophilicity, porosity, and permeability of the membrane was determined. Membrane performance was evaluated for removal of lead ions in dynamic filtration and static adsorption. The membranes were found as effective adsorptive filters for removal of lead ions via interactions between active sites of nanocomposite in membrane structure and lead ions during filtration. Results of batch experiments proved adsorptive mechanism of membranes for removal of lead ions with the maximum adsorption capacity of 19.6 mg/g.

Selective removal of Cr(VI) from aqueous solution by adsorption on mangosteen peel

Mangosteen peel, rich in polyphenolic compounds, was used to prepare the adsorbent exhibiting highly selective adsorption for Cr(VI) over other metal ions such as Pb(2+), Fe(3+), Zn(2+), Cd(2+), and Cr(3+) at the pH values of 1∼4. The chemical modification method proposed by using calcium hydroxide is quite cost-effective and ecofriendly without using any toxic reagents or causing any secondary pollution. The adsorption isotherm results revealed that the adsorption of Cr(VI) on the gel fit well the Langmuir adsorption model, and the maximum adsorption capacity for Cr(VI) at pH levels 1, 2, 3, and 4 was evaluated to be 2.46, 2.44, 1.99, and 2.14 mol/kg, respectively. The adsorption mechanism for Cr(VI) on the saponified gel was verified to follow an esterifiaction reaction coupled with the reduction of Cr(VI) to Cr(III) in which H(+) plays a role of promoter. Thus, modified mangosteen peel gel has the prominent selectivity and low cost for Cr(VI) removal.