Abstract
In the present study, the straw ash (SA) was proposed to remove phosphate and fluoride from aqueous solution. The effects of SA dosage, initial contaminants concentration and initial pH on removal efficiency, adsorption kinetics and isotherms were investigated in batch experiments. The removal mechanisms were also discussed. The results show that solution pH was a critical parameter for the adsorption and the removal efficiency decreased with the increase of initial pH. At initial solution pH of 2, the removal efficiency of SA (25 g/L) for phosphate (200 mg/L) achieved 88.20%, and the fluoride (100 mg/L) removal rate by SA (50 g/L) was 87.52%. The adsorption for phosphate/fluoride followed the pseudo?second?order kinetic model. The adsorption isotherm data were well fitted by the Langmuir model, and the maximum adsorption capacity of SA reached 92.16 mg/g for phosphate and 66.23 mg/g for fluoride. The SEM-EDS and XRD tests show that phosphate/fluoride were mainly removed by chemically precipitating as CaHPO4, Ca4H(PO4)3·2.5H2O, Ca5(PO4)3(OH) and AlF3, CaF2 on the SA surface. Electrostatic attraction and ligand exchange with hydroxyl groups also exited in the removal process. Besides, SA has been proved to be a promising adsorbent for the treatment of industrial wastewater contaminated with phosphate and fluoride.
Graphical abstract
Introduction
Phosphate and fluoride are important contaminants in water bodies. The discharging of phosphate and fluoride mainly come from industrial activities. For instance, the phosphate and fluoride concentration of wastewater generating from fertilizer production could achieve 4540 and 9720 mg·L?1, respectively (Bagastyo et al., 2017). And wastewater mixed with fluoride and phosphate is also produced in semiconductor manufacturing (Park et al., 2008). Surveys revealed that high level of phosphate and fluoride in groundwater occurred in many areas around the word such as China, Mexico and India (Kong et al., 2019). The excessive phosphate in water causes eutrophication and enormous death of aquatic lives, while long-term intake of fluoride often results in dental and skeletal fluorosis (Koilraj and Sasaki, 2017; Zhao et al., 2018). The International Agency for Research on Cancer (IARC) has classified phosphate and fluoride as carcinogenic to humans (International Agency for Research on Cancer, 2021). Moreover, the coexistence of phosphate and fluoride exposes more severe damage to human security (Kong et al., 2019). Therefore, it has become a global environmental requirement to remove the phosphate and fluoride from water systems.
Several technologies such as ion exchange (Dong et al., 2020; Grzegorzek et al., 2020), adsorption (Murambasvina and Mahamadi, 2020; Oginni et al., 2020), chemical precipitation (Huang et al., 2017) and coagulation (Bakshi et al., 2020; Dubey et al., 2018) have been used for phosphate and fluoride removal. However, most of these techniques have disadvantages and limitations in practical application for the high energy consumption and complex operation process. Adsorption is considered as a promising technique for the removal of pollutants from aqueous solution with multiple virtues of wide material availability, easy operation and low operational cost (Saadat et al., 2018). In recent years, diverse adsorbents including metal oxides/hydroxides, biochar, industrial and agricultural by?products have been developed for phosphate and fluoride removal from wastewater (Goswami and Kumar, 2018; Kong et al., 2020; Kumari et al., 2020; Liu et al., 2018; Ye et al., 2020). Solid wastes, such as steel slag (Claveau-Mallet et al., 2013; Sellner et al., 2019), fly ash (Hermassi et al., 2017; Ye et al., 2019) and basic oxygen furnace slag (Islam and Patel, 2011; Xue et al., 2009), have attracted extensive attention among these sorbents on account of their easy?gained and low?cost. These solid wastes are usually composed of oxides, such as SiO2, MgO, CaO, Fe2O3 and Al2O3, that would promote the removal of phosphate and fluoride through electrostatic attraction, precipitation, and ligand exchange (Lee et al., 2020; Li et al., 2020b; Xu et al., 2015; Yin et al., 2017). Additionally, the large specific surface areas and abundant porous structure of these solid wastes can greatly enhance their adsorption capacity (Qiu and Duan, 2019).
Straw ash (SA) is a kind of solid waste after the thermo?chemical transformation of straw, and has the characteristics of low density, high porosity and large surface area. SA has been proved to be a promising adsorbent for the removal of heavy metals (Arshadi et al., 2014; Zhang et al., 2019). It could immobilize heavy metals through chemical precipitation, ion exchange and surface complexation. Besides, the alkaline of SA equips it with excellent acid neutralization capacity. However, there have been no relevant reports on the use of SA as phosphate and fluoride adsorption material. Previous studies have showed that alkaline residue is an effective adsorbent for the removal of anionic dye and phosphate (Yan et al., 2014). And the main components of SA (i.e., CaO, Fe2O3, SiO2 and Al2O3) enable it to adsorb or precipitate phosphate and fluoride. Therefore, SA can be considered as a potential adsorbent for the removal of phosphate and fluoride from aqueous solution.
To explore the feasibility of the SA to be used as adsorbent for phosphate and fluoride removal, the effects and mechanisms of the SA on removing phosphate and fluoride from artificially acid solutions were evaluated in this work for the first time. The aims are to exhibit the potential application of the SA for the treatment of industrial wastewater contaminated with phosphate and fluoride, and provide theoretical support for its practical application.
Figures
-
-
-
Effect of straw ash dosage on removal efficiency of phosphate and fluoride. Conditions: initial concentration of 200mg/L for phosphate and 100mg/L for fluoride, initial pH of 2.0, contact time of 120m… -
Effect of initial pH on removal efficiency and equilibrium pH ((a) for phosphate and (b) for fluoride). Conditions: contact time of 120min, straw ash of 25g/L for 200mg/L phosphate and 50g/L for 100mg… -
Adsorption kinetics of the straw ash for phosphate (a) and fluoride (b). Conditions: initial pH of 2.0, straw ash of 25g/L for 200mg/L phosphate and 50g/L for 100mg/L fluoride, contact time of 5, 15, … -
Adsorption isotherms of straw ash for phosphate (a) and fluoride (b). Conditions: initial pH of 2.0, contact time of 120min, straw ash of 10g/L for phosphate and fluoride, initial concentration of 200… -
Zeta potential of straw ash as a function of pH in the absence or presence of either phosphate or fluoride.
Section snippets
Materials and reagents
The straw ash (SA) was obtained from Huaneng thermal power plant, Jilin Province, China. The powder sample was dried at 105 °C for 120 min, ground into less than 100 mesh particles and thoroughly homogenized before used. All chemicals used were in analytical grade.
Characterization methods
The main chemical compositions of SA were examined using quantitative analysis methods. The silicon content of SA was determined by perchloric acid dehydration gravimetric method described in Chinese standard GB/T 1509–2016. Mixed
Chemical compositions and heavy metals leaching concentration of straw ash
The main chemical compositions of SA are presented in Table 2. It can be seen that the SA mainly consisted of SiO2, K2O, CaO, Al2O3 and MgO. Considering of environmental risks, the leaching toxicity of heavy metals in SA were tested. According to the data in Table 3, a negligible amount of Pb, Zn, Cu, Cd, Ni and Cr leached from SA, illustrating that SA is an environmentally friendly material for the removal of phosphate and fluoride from aqueous solution.
Effect of adsorbent dosage
The effects of the SA dosage on the
Conclusions
The present study shows that the SA is a cost-effective and environmentally friendly adsorbent for the removal of phosphate and fluoride from aqueous solution. The solution pH was a critical parameter for the removal of phosphate/fluoride and the removal efficiency decreased with the increase of initial pH. At initial solution pH of 2, the removal efficiency of SA (25 g/L) for phosphate (200 mg/L) achieved 88.20%, and the fluoride (100 mg/L) removal rate by SA (50 g/L) was 87.52%. The
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
The authors gratefully acknowledge the financial support from State Key Laboratory of Mineral Processing (BGRIMM-KJSKL-2019-15), and also gratefully thank analytical and Testing Center of University of Science and Technology Beijing, which supplied us the facilities to ful?ll the measurement.
References (46)
- et al.
Equilibrium and kinetics modeling of fluoride adsorption onto activated alumina, alum and brick powder
Groundw. Sustain. Dev.
(2018) - et al.
Kinetic, equilibrium and thermodynamic investigations of Ni(II), Cd(II), Cu(II) and Co(II) adsorption on barley straw ash
Water Resour. Ind.
(2014) - et al.
Electrodialytic removal of fluoride and calcium ions to recover phosphate from fertilizer industry wastewater
Sustain. Environ. Res.
(2017) - et al.
Electrocoagulation for removal of phosphate from aqueous solution: statistical modeling and techno-economic study
J. Clean. Prod.
(2020) - et al.
Removal of phosphorus, fluoride and metals from a gypsum mining leachate using steel slag filters
Water Res.
(2013) - et al.
Excellent disinfection and fluoride removal using bifunctional nanocomposite
Chem. Eng. J.
(2018) - et al.
Experimental investigation of Al-F species formation and transformation during coagulation for fluoride removal using alum and PACl
J. Mol. Liq.
(2018) - et al.
Removal of fluoride from aqueous solution using nanoscale rice husk biochar
Groundw. Sustain. Dev.
(2018) - et al.
Removal of fluoride from multicomponent water solutions with the use of monovalent selective ion-exchange membranes
Sci. Total Environ.
(2020) - et al.
Fly ash as reactive sorbent for phosphate removal from treated waste water as a potential slow release fertilizer
J. Environ. Chem. Eng.
(2017) -
- et al.
Investigation on the simultaneous removal of fluoride, ammonia nitrogen and phosphate from semiconductor wastewater using chemical precipitation
Chem. Eng. J.
(2017) - et al.
Thermal activation of basic oxygen furnace slag and evaluation of its fluoride removal efficiency
Chem. Eng. J.
(2011) - et al.
Selective removal of phosphate using La-porous carbon composites from aqueous solutions: batch and column studies
Chem. Eng. J.
(2017) - et al.
Synchronous phosphate and fluoride removal from water by 3D rice-like lanthanum-doped La@MgAl nanocomposites
Chem. Eng. J.
(2019) - et al.
Calcium and zirconium modified acid activated alumina for adsorptive removal of fluoride: performance evaluation, kinetics, isotherm, characterization and industrial wastewater treatment
Adv. Powder Technol.
(2020) - et al.
Experimental and model study for fluoride removal by thermally activated sepiolite
Chemosphere
(2020) - et al.
Removal and recovery of phosphate and fluoride from water with reusable mesoporous Fe3O4@mSiO2@mLDH composites as sorbents
J. Hazard Mater.
(2020) - et al.
Removal of phosphate from aqueous solution by dolomite-modified biochar derived from urban dewatered sewage sludge
Sci. Total Environ.
(2019) - et al.
Enhanced phosphate removal from aqueous solution using resourceable nano-CaO2/BC composite: behaviors and mechanisms
Sci. Total Environ.
(2020) - et al.
Review of metal (hydr)oxide and other adsorptive materials for phosphate removal from water
J. Environ. Chem. Eng.
(2018) - et al.
Adsorption recovery of phosphate from aqueous solution by CaO-biochar composites prepared from eggshell and rice straw
Sci. Total Environ.
(2019) - et al.
Cement paste column for simultaneous removal of fluoride, phosphate, and nitrate in acidic wastewater
Chemosphere
(2008) - et al.
Synthesis of industrial solid wastes/biochar composites and their use for adsorption of phosphate: from surface properties to sorption mechanism
Colloids Surf., A
(2019)
There are more references available in the full text version of this article.
*Original study online at https://www.sciencedirect.com/science/article/abs/pii/S2352801X21000837
- et al.