Novel adsorbent derived from sludge of paper industry for removal of cesium ion in water

Metal ion contamination has been a public concern due to its negative impact on human health and the environment. Cesium (Cs), a harmful metal ion, can cause cell damage; acute radiation syndrome includes nausea, vomiting, diarrhea, bleeding, and, in extreme cases, death. As a result, removing cesium ion from water is critical. This research aims to examine the capacity of a novel adsorbent derived from paper industry solid waste to remove cesium ion from water. The adsorption process was carried out with some variables including adsorbent dose, solution of pH, contact time, initial Cs concentration, and adsorbent form. According to characterization data, paper industry sludge contains elements such as SiO2 (28.1%), CaO (21.8%), Al2O3 (16.1%), and Fe2O3 (12%), among others. The surface area of the adsorbent is 100 m2/g and a diameter of 3.8 nm. Following equilibrium, the current study discovered that the developed adsorbent has the highest cesium removal, up to 79% for 10 mg/L of Cs initial. The novel adsorbent has high adsorption removal and may be a promising adsorbent material for metal ion removal in water.


Introduction
The discharge of radioactive elements into the environment, particularly cesium isotopes, endangers public health and the ecological equilibrium [1].Notable instances, such as the 2011 Fukushima Daiichi nuclear accident, have emphasized the critical need to develop efficient measures for reducing the spread of cesium contamination in water bodies.Cesium-137, in particular, provides a continuous difficulty that necessitates sophisticated removal procedures due to its lengthy half-life [2] and [3].
Adsorption has emerged as a promising method for removing cesium ions from aqueous solutions as a basic physicochemical event [4] and [5].The interaction of cesium ions with the solid surfaces of adsorbent materials causes their immobilization and subsequent separation from the water phase.For this purpose, several adsorbent materials have been studied, including zeolites, activated carbon, clays, metal oxides, and organic polymers, each with unique surface area, porosity, and functional groups [6] and [7].Researchers have made tremendous progress in developing novel adsorbents with improved cesium adsorption capabilities, selectivity, and recyclability throughout the years.Studying these innovative IOP Publishing doi:10.1088/1755-1315/1263/1/012059 2 materials is an important step toward improving water treatment technology for effective and long-term cesium removal.This study intends to add to the expanding body of knowledge in this sector by evaluating the adsorption performance of the novel adsorbents based on paper sludge and comparing their efficacy to that of traditional materials.
The extensive laboratory investigations, including batch adsorption studies, effect of adsorbent dose, pH of a solution, contact time and desorption of cesium ion were studied.Adsorbent materials will be characterized utilizing modern methods such as scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and surface area analysis.In addition, this study will explore how solution pH, temperature, and starting cesium concentration affect the adsorption effectiveness of the chosen materials.
The study's findings have the potential to pave the way for unique and effective cesium removal techniques, therefore preserving freshwater resources and protecting human health.As worries about water quality grow, the importance of this study rests in its contribution to sustainable water treatment procedures in the face of rising issues posed by environmental contamination.

The preparation of the adsorbent, chemical and instrument for adsorption
Paper sludge, a solid waste from the paper industry, was utilized to make the novel adsorbent employed in this study.The paper sludge used in this study was obtained from one of the papers industries in Sapporo City, Hokkaido, Japan.Paper sludge was created during the papermaking process.The paper sludge was processed at 950°C after dehydration and drying to generate paper sludge carbon.The carbon from paper sludge was rinsed with distilled water and dried for 24 hours at 100°C.The paper sludge was crushed into powdery adsorbent and screened through a 1 mm sieve after cooling at room temperature.Phosphoric acid was utilized to treat paper sludge to improve the adsorption of the adsorbent for cesium ion in water.Cesium standard from WAKO Pure Chemical Co (Osaka, Japan) was used to make a cesium ion (Cs2+) stock solution.The SEM (JEOL JSM-6360 LA, Japan), FT/IR-4100 FT-IR Spectrometer (JASCO, Japan), BELSORP-mini (BEL Japan Inc, Japan), and Element analyzer (MICRO CORDER JM10, Yanaco, Japan) were used to know the porosity, surface area, functional groups, pore size, density, and major components of paper sludge.

The process of adsorption
The batch system was used in this work to carry out the adsorption procedure.The ability and ideal conditions for adsorption using this adsorbent were evaluated based on some variables such as adsorbent mass, pH, stirring duration, and initial cesium ion concentration.To determine the impact of adsorbent mass, 50 ml of cesium solution was stirred at 1000 rpm for 120 minutes with a shaker (Eyela Cute Mixer CM-1000).The effect of pH on cesium ion adsorption was examined using pH 6 and 8 solutions (based on a previous study).Acetic acid, HNO3, and NaOH were used to achieve the necessary pH levels.Shaking duration ranging from 2 to 24 hours was used to determine the effect of shaking time on cesium ion adsorption.After reaching equilibrium, the solution was spun at 4000 rpm for 5 minutes with a centrifuge (IEC61010-2-020, KUBOTA, Japan).Then the cesium ion concentration was tested with an ICP MS and Atomic Absorption Spectrophotometer (Flame AAS) (HITACHI A-2000, Japan) with the addition of potassium solution (high concentration) to avoid the disturbances in the solution.

The characteristic of adsorbent based on solid waste of paper industry
The paper sludge adsorbent has some functional groups such as hydroxyl, carboxyl and amine, as shown in the result of the FTIR test (Figure1).FTIR test is a sophisticated analytical method used to analyze the interaction between adsorbent materials and cesium ions during the adsorption process in water.FTIR spectra provide vital information on the functional group's presence on the adsorbent's surface and can provide insights into the chemical changes that occur during cesium ion adsorption.
The functional groups on the surface of the adsorbent material may be identified using FTIR spectra.Because of their propensity to create complexation or ion-exchange contacts with cesium ions, functional groups such as hydroxyl groups (OH) from cellulose [8], carboxylic acids (COOH) at peak 1650, amines (NH2), and silanol groups (Si-OH) play an important role in cesium ion adsorption.By comparing the FTIR spectra before and after cesium ion adsorption, it is feasible to establish whether any functional groups are involved in the adsorption process.SEM pictures illustrate the surface morphology of the adsorbent material.SEM micrographs will reveal the surface texture, which might be smooth, rough, or porous.The effect of adsorbent treatment using phosphoric acid (Figure 2) indicated that the surface of the adsorbent is not significantly changing.Smooth surfaces may indicate a homogenous material, whereas rough or porous surfaces may indicate a more uneven or heterogeneous structure.The surface shape can alter the accessible surface area for adsorption and hence the efficacy of cesium ion removal.

Removal of Cesium ion in water on different adsorbent dose
The impact of adsorbent dose on Cs removal is shown in Figure 3 where the Cs removal increase with the increase of adsorbent mass.Cs initial 50 mg/l adsorption process's overall performance.Understanding this phenomenon is critical for creating effective cesium removal systems and optimizing adsorbent usage in actual applications.Adsorption capacity typically increases as adsorbent mass increases.More adsorption sites become available to attract and immobilize cesium ions when the amount of adsorbent material in contact with the cesium-containing solution rises, causing a more incredible amount of cesium ions to be taken from the water until all possible adsorption sites are saturated [9].

Removal of Cesium ion in water on different shaking time
The impact of shaking time was conducted six times to prove the reproducibility of data (Figure 4), where its capacity increases with the increase of shaking time.This impact relates to how the duration of the mixing process, also known as agitation or shaking, affects the adsorption process's effectiveness.In batch adsorption tests, stirring duration is a crucial parameter when the adsorbent is combined with the cesiumcontaining solution to ensure sufficient contact between the two phases.Understanding this impact is critical for improving the adsorption process and identifying the optimal contact period for maximal cesium ion elimination.The shaking time directly affects the rate at which cesium ions are adsorbed onto the adsorbent material.The number of cesium ions bound to the adsorption sites on the surface of the adsorbent rapidly increases during the early adsorption phases.The rate of cesium ion adsorption slows as the shaking period rises and the system approaches equilibrium [10].

Removal of Cesium ion in water on different pH of solution
The adsorption performance of cesium ion in water is influenced by the pH of the solution, where increasing the pH of the solution resulting better adsorption capacity.The influence of pH on the adsorption of cesium ion is shown in Figure 5.The pH of the solution is an important element that determines the adsorption of cesium ions in water.Changes in the surface charge of the adsorbent material and the cesium ions in the solution are principally responsible for the pH influence on cesium ion adsorption.Understanding this impact is critical for improving the cesium removal process and creating effective water treatment adsorption systems.The adsorbent material's surface charge is critical in cesium ion adsorption.The surface of the adsorbent can be positively charged (under acidic circumstances), negatively charged (under basic conditions), or electrically neutral (around the material's isoelectric point) at different pH levels.The attraction or repulsion forces between the cesium ions and the adsorbent are determined by the surface charge, which influences the adsorption capacity [11][12][13].
Cesium ions (Cs+) can also be ionized in a pH-dependent manner.Cesium ions are less likely to form hydroxide complexes (CsOH) under lower pH values (acidic environments) and tend to remain as Cs+ ions.As the pH rises (basic circumstances), the production of CsOH complexes becomes more favorable, altering the cesium speciation in the solution.The interaction of cesium ions with the adsorbent surface is affected by changes in cesium ion speciation.Hydrogen ions (H+) and hydroxide ions (OH-) coexist in aqueous solutions, impacting the pH value.An oversupply of H+ ions can compete with cesium ions for accessible adsorption sites on the adsorbent surface in low pH (acidic) circumstances.Similarly, in high pH (basic) circumstances, excess OH-ions might compete for adsorption with cesium ions, reducing total adsorption capacity [7].
The ionization state of functional groups on the adsorbent surface can also be affected by the pH of the solution.Because of their propensity to create complexation or ion-exchange contacts with cesium ions, certain functional groups, such as carboxylic acids, amines, or hydroxyl groups, play an significant role in cesium ion adsorption.The degree of ionization of these functional groups varies with pH, influencing total adsorption behavior.

Desorption of Cs on varied pH solution
The desorption of Cesium on different pH of the solution is shown in Figure 6, where it was clear that acidic conditions resulted in higher Cs desorption.Cesium ion desorption in water refers to the process by which cesium ions that had previously been adsorbed onto an adsorbent material are released or removed from the adsorbent's surface and returned to the aqueous solution.Desorption is an important stage in the regeneration  Depending on the nature of the adsorbent and the interactions between the cesium ions and the adsorbent surface, desorption can occur in various ways.When ion exchange interactions occur during adsorption, desorption occurs when other cations in the solution compete with cesium ions on the adsorbent surface.Typically, this is accomplished by adjusting the pH of the solution or by utilizing solutions with more significant concentrations of competing ions.Introducing particular desorption agents into the solution, such as salts or complexing agents, can efficiently remove cesium ions from the adsorbent surface.The desorption agent generates stronger compounds with cesium ions than the adsorbent, allowing cesium to be released into the solution more easily.Changing the pH of the solution can influence the charge on the adsorbent surface, altering the electrostatic interactions between the adsorbent and cesium ions.Shifting the pH to a specific range might enhance desorption in some circumstances [14] and [15].The result of the current study clearly shows that the desorption of cesium ion decreases by increasing the pH of the solution.The desorption of cesium ion is lowest using distilled water (DW).

Conclusion
Removing cesium ion in water using a new adsorbent based on paper industry solid waste appears promising.The adsorbent shows effective adsorption removal up to 79% for initial Cs of 10 mg/L.Some factors impact adsorption performance, such as adsorbent dosage, contact duration, solution pH, and the existence of some functional groups in the adsorbent material.Cs desorption is regulated by several factors, including the pH of the solution, with acidic conditions resulting in more desorption.

Figure 1 .
Figure 1.FTIR spectra of the adsorbent before and after treatment with phosphoric acid.

Figure 2 .
Figure 2. SEM spectra of adsorbent derived from paper sludge (a) before treatment with phosphoric acid and (b) after treatment with phosphoric acid.

Figure 3 .
Figure 3.The effect of adsorbent dose on cesium removal in water using paper sludge adsorbent.

Figure 4 .
Figure 4.The effect of contact time on the cesium removal using paper sludge adsorbent.

Figure 5 .
Figure 5. Adsorption of cesium ion in water with different pH solution.
.1088/1755-1315/1263/1/012059 7 and reusability of cesium removal adsorbents.Understanding the components and mechanisms that influence desorption is critical to improving the overall effectiveness of cesium ion removal systems.

Figure 6 .
Figure 6.The desorption of cesium ion in different pH solution.