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Review

Advances in the Study of Heavy Metal Adsorption from Water and Soil by Modified Biochar

by
Yizhuo Wang
1,
He Li
1,* and
Shaohua Lin
2
1
School of Civil Engineering, Southeast University, Nanjing 210096, China
2
School of Civil Engineering, Nanjing Forestry University, Nanjing 210037, China
*
Author to whom correspondence should be addressed.
Water 2022, 14(23), 3894; https://doi.org/10.3390/w14233894
Submission received: 24 October 2022 / Revised: 22 November 2022 / Accepted: 25 November 2022 / Published: 29 November 2022
(This article belongs to the Special Issue Advances in Wastewater Treatment: Resources Recovery, Energy Neutralization, Water Reuse)
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Abstract

:
Heavy metal contamination in water and soil has gradually become a concern with the development of industry in recent years and may pose a serious threat to human health if left untreated. Biochar is commonly used as an adsorbent/immobilizer of heavy metals from water and substrates because of its wide—ranging raw materials, low production cost, and good adsorption performance. Based on the adsorption mechanism of biochar, this paper analyzes different modification methods of biochar, aiming to provide an effective material for the treatment of heavy metals from water and sediment and provide a certain reference for its application to practical projects.

1. Introduction

With the continuous improvement in people’s day—to—day life and industry production levels, the pollution of water and sediment by heavy metals is also deepening. At the same time, the sources of heavy metals are wide—ranging, mainly from industrial production industries such as the machinery processing industry, steel, non—ferrous metal smelting industry, etc. In addition, the emission of automobile exhaust, the disposal of waste batteries, and the abuse of agricultural fertilizers in our daily life can also cause serious heavy metal pollution to river—bottom mud [1,2].
The composition of the surface river and lake sediments is complex, mainly including clay, sediment, organic matter, and various mineral bodies [3,4]. Heavy metals in sediment mainly originate from polluted water bodies, and a series of transformation and migration processes such as adsorption–desorption, precipitation–dissolution, complexation–decomplexation, ion exchange, and redox occur between the sediment and the water body [5].
Because of their slow mobility and long residence time, heavy metals in the sediment are not degraded easily by microorganisms [6], and if they are not treated in time, they will become a “new source of pollution”, polluting the water body twice, poisoning the plants and animals in the water and then further endangering human life and health through transmission via the food chain [7]. The problem of how to treat heavy metals in river sediments and water bodies has become a pressing one [8].
Long—term exposure to heavy metal ions can cause serious harm to the human body, e.g., the activity of enzymes, the nervous system, and some organs with detoxification functions will be affected [9]. The use of water contaminated with heavy metals can cause direct harm to the human body; for example, in the 1950s and 1960s, Japanese production mines exceeded the Cd(II) standard in nearby waters, causing some nearby residents to suffer from “bone pain”, leading to osteochondrosis and general pain. Further, the accidental release of chemicals containing Hg(II) in Taiwan has contaminated the soil in several locations, and the consumption of crops grown on these soils can cause the heavy metal Hg(II) in the human body to exceed the limit. When people consume Hg(II)—poisoned fish, they will suffer from neurological toxicity, impaired sensation at the ends of their limbs, and narrowed vision [10].
Adsorption is the most commonly used method for treating heavy metals in water bodies and sediments, with the main advantages of being renewable, low cost, creating no “secondary pollution”, and suitable for treating various concentrations of wastewater.
Biochar is a carbon—rich product obtained by charring biomass, and it has been widely studied for its advantages of low price and a wide range of sources. With its large porosity as well as specific surface area and the presence of many functional groups on its surface, it is an efficient and low—cost adsorbent and is often widely used to remove heavy metal pollutants from water [11]. Singh et al. conducted batch experiments on Cu(II), Cr(VI), Cd(II), and Pb(II) to investigate the effects of contact time, adsorbent dose, pH, and charring temperature on the adsorption of heavy metals. The experimental results showed that the adsorption capacity was positively correlated with the adsorption time in the first 20 min but gradually tended to reach equilibrium after 20 min. The adsorbent dose and pyrolysis temperature were positively correlated with the removal effect of biochar for heavy metals, and the maximum removal efficiency of biochar could reach 99.86% at pH = 4 [12]. Park et al. investigated the adsorption of heavy metals on sesame straw charcoal (SSB) and compared its adsorption of single and multiple metals. They found that SSB had superior adsorption effects on heavy metals, and the adsorption capacities of SSB for single heavy metals were, in descending order, Pb(II) > Cu(II) > Cr(VI) > Zn(II) > Cd(II), and for polymetals were, in descending order, Pb(II) > Cd(II) > Cr(VI) > Cu(II). The adsorption capacity for polymetallics was much greater than for monometallics [13]. Although biochar has a certain adsorption effect on heavy metals, the adsorption capacity is relatively limited, and in order to improve the utilization of biochar, biochar should be further modified to effectively enhance its remediation function [14].

2. Modified Carbon Properties and Types

Biochar is a black carbon—containing solid obtained by high—temperature pyrolysis of biomass under anaerobic or oxygen—limited conditions. Biochar contains a large number of pores and rich functional groups, with a large specific surface area and high stability, and has been widely used in soil remediation, carbon sequestration, and wastewater treatment [15]. However, the light mass, small powder particles, and single composition of biochar compromise the effectiveness of the adsorption of heavy metals and organic pollutants, etc., and recovery in water and soil is limited. Modified biochar can compensate for some of the shortcomings of single biochar and improve the adsorption effect, so modified biochar materials have received much attention in recent years.
There are usually two types of modifying biochar: one is to modify the prepared biochar by impregnation with chemicals or co—precipitation with metals; the other is to prepare biomass raw materials by mixing them with modification reagents and preparing them by high—temperature pyrolysis. Biochar modification includes surface structure modification and surface chemical modification. Surface structure modification is mainly to change the pore structure of biochar to increase the specific surface area in order to increase the adsorption capacity; surface chemical modification is to modify the functional groups on the surface of biochar to increase the adsorption sites and improve the adsorption effect. The general preparation process of mixing biomass raw materials with other reagents for pyrolysis modification includes mixing, filtration, drying, pyrolysis, and debinding.

3. Mechanism of Heavy Metal Adsorption by Biochar and Modified Biochar

The main adsorption mechanisms of biochar and modified biochar for heavy metals include physical adsorption and chemical adsorption. Physical adsorption is mainly based on the specific surface area or van der Waals force. However, they can be ignored because of their weak effects [16]. The specific adsorption mechanisms of biochar and modified biochar for heavy metals are shown below.
(1)
Surface adsorption
The surface of biochar contains many acidic groups, such as carboxyl, phenolic hydroxyl, etc., which can form specific metal complexes with heavy metal ions in water and soil to form active adsorption sites, so that surface adsorption can be carried out. The main influencing factors are the chemical bond on the surface of biochar, the diffusion effect of heavy metal ions, etc. [17,18,19,20]. Linbo Qian et al. used rice straw to prepare biochar colloids and found that the main mechanism of adsorption was that the surface of the biochar gel made from rice straw had a large number of oxygen—containing functional groups and minerals at a high carbonization temperature, which could be used as adsorption sites for Cr(III) and Cd(II) [20].
(2)
Electrostatic adsorption
Electrostatic adsorption is the essence of forming ionic bonds, which can be influenced by zeta potential and pH [21]. Chen Zhuang et al. used iron nitrate—modified reed biochar (FeBC) and found that the removal rate of the modified charcoal for Cr(VI) could reach 94.52%, where the adsorption mechanism was mainly due to the electrostatic adsorption of positive charges on the surface of modified FeBC with Cr(VI) and Cd(II) [22]. Xuejiao Tong studied the effect of zeta potential and pH on the electrostatic adsorption of crop straw char on heavy metal Cu(II), and the experimental results showed that the absolute value of the negative zeta potential increased with the increase in pH, i.e., more and more anions on the biochar surface, thus helping with the adsorption of Cu(II) by the biochar [23].
(3)
Ion exchange
The essence of ion exchange is the exchange reaction between charged cations and protons on the surface of biochar and dissolved heavy metal ions under suitable pH conditions [24,25]. The main biochar surface cations that can exchange ions with heavy metal ions are potassium, calcium, sodium, and magnesium ions. The nature of the functional groups on the surface of biochar, the size of the contaminants, and the nature of the charge all have an effect on ion exchange. Li A Y et al. prepared six types of biochar (BSB, CSB, FSB, CFSB, MSB, and TSB) with different raw materials, in which magnesium ions were loaded by the impregnation method. The experimental results showed that these types of biochar had good adsorption effects on heavy metals such as Cd(II), Cu(II), and Pb(II). Biochar contains a large number of magnesium ions and functional groups that can form complexes with metal ions to perform a strong ion exchange. Therefore, mineral precipitation and cation exchange play a dominant role in the adsorption process [26]. However, when the concentration of metal ions such as potassium, calcium, sodium, and magnesium ions on the surface of biochar is too high, it will compete with heavy metal ions, thus reducing the effect of ion exchange and hindering the adsorption process of heavy metals, so the effect of ion exchange is related to the concentration of metal ions on the surface of biochar [27,28].
(4)
Chemical precipitation
The minerals in biochar contain anions such as OH−, SO42−, SO32−, and CO32−, which provide a large number of adsorption sites for heavy metals and react with them to form water—insoluble precipitates [29,30]. When the elemental composition of biochar has a high content of P, S, Si, and Al, it might mean that there are more mineral acid ions on its surface, which can have a positive effect on the removal of heavy metals by biochar. Xiaoyun et al. prepared rice husk biochar (RHBC) and cow dung biochar (DMBC) using rice husk and cow dung as raw materials and used them as adsorbents to remove Pb(II), Cu(II), Zn(II), and Cd(II) from aqueous solutions. The experimental results showed that DMBC had better adsorption capacity for these four heavy metals compared to RHBC, and its adsorption mechanism was mainly due to the fact that the surface of DMBC was rich in anions such as CO32− and PO43−, which participated in the adsorption reaction and provided reaction sites in contact with Pb(II) and further formed precipitation, thus removing Pb(II) from water [31]. Zama, E.F et al. investigated the effect of biochar prepared from various raw materials at different charring temperatures for the removal of heavy metals Pb(II) and Cd(II); the experimental results showed that the best adsorption effect for Pb(II) and Cd(II) was achieved when the charring temperature was 700 °C for rice stalk charcoal and the adsorption capacity could be distributed up to 126.58 mg/g and 60.61 mg/g, as shown by the XRD pattern. The analysis showed that the biochar indicated the presence of a large amount of CO32−, PO43−, and SiO44, which can produce chemical precipitation with heavy metals [32].
The specific mechanisms of biochar with heavy metals are shown in Figure 1, the behavior of biochar with reference to metals are shown in Figure 2 and Figure 3, and the adsorption mechanisms and principles of biochar, as well as modified biochar, are shown in Table 1:
The surface of biochar is smooth in the macro view, but in fact, its surface is often uneven at the atomic level. The atoms and molecules on the solid surface are subject to uneven forces, but because the position of the molecules on the solid surface is fixed and cannot be moved like the molecules on the liquid surface, the uneven forces are difficult to balance.
Due to the asymmetry of the force exerted on the atoms on the solid surface and the non—uniformity of the surface structure, the solid surface layer material receives a pull pointing inward, resulting in an unbalanced force field.
Because the atoms on the solid surface are positioned, it is not possible to balance the force field by shrinking the surface, but it is possible to use the residual force on the surface to capture other metal ions from the surrounding medium so that the force imbalance can be compensated to a certain extent, and adsorption can be generated.

4. Biochar Modification Methods and Their Principles

Although biochar has a certain adsorption effect on heavy metals, the adsorption capacity is relatively limited. In order to improve the utilization of biochar, it is necessary to modify biochar further to effectively enhance the remediation function of biochar [33]. The modification methods of biochar include physical modification, redox modification, acid–base surface modification, adsorbent compound modification, and activation modification. These methods can improve the adsorption capacity of biochar for heavy metals by increasing the number of functional groups on the surface of biochar, the biochar’s specific surface area, and pore capacity. The specific modified materials and modification principles used in each modification method are shown in Table 2.

5. Application of Biochar and Modified Biochar to Remove Heavy Metals from Water

(1) Removal of heavy metals from water by biochar
Biochar is a carbon—rich product obtained by charring biomass that has high porosity and a large specific surface area, and many functional groups exist on its surface, making it an efficient and low—cost adsorbent that is often widely used to remove heavy metal pollutants from water. The raw material selected for biochar and the charring temperature are the key factors that determine the chemical and physical properties of the biochar [41].
The effectiveness of biochar in adsorbing heavy metals in water varies depending on the raw material. A study showed that the adsorption of heavy metal Cu(II) by coconut shell charcoal, bamboo charcoal, and wood charcoal was effective; the adsorption processes of coconut shell charcoal and bamboo charcoal were more consistent with the results of the fitted Freundlich isothermal adsorption model, and the adsorption of wood charcoal was more consistent with the results of the fitted Langmuir isothermal model [42]. Shaon Kumar Das et al. selected four kinds of raw materials, such as corn stalks as raw materials and prepared four different types of biochar for the adsorption of Cd(II), Pb(II), Ni(II), Zn(II), and Cd(II) from water at a charring temperature of 600 °C. The experiments showed that each biochar was effective in the removal of heavy metal mixtures from water. The adsorption capacity of the biochar made from different materials varied for each metal. The removal rates of heavy metals by corn stalk charcoal, pine needle tree charcoal, BGB, and LCB were Cu(II) > Pb(II) > Zn(II) > Cd(II) > Ni(II); Ni(II) > Cd(II) > Zn(II) > Cn(II) > Cu(II); Cd(II) > Zn(II) > Pb(II) > Cu (II) > Ni(II); and Cu(I) > Cd(I) > Pb(I) > Zn(I), respectively [43].
Charring temperature is also a key factor affecting the ability of biochar to adsorb heavy metals. Jia Y et al. used rice husk and cotton straw to make biochar at charring conditions of 300, 400, 500, 600, and 700 °C. The experimental results showed that the charring temperature was negatively correlated with the biochar yield and positively correlated with the ash content, and the pH also changed from acidic through neutral to alkaline or even strongly alkaline with the increase in charring temperature, while the aromaticity of the biochar gradually increased, the number of oxygen—containing functional groups decreased and the structure became more stable, but the hydrophilicity and polarity decreased [44]. Xiao Y et al. used 300, 450, and 600 °C for charring to determine the optimal temperature to improve the binding capacity of biochar. The experimental results showed that the charring temperature had different effects on the elemental composition, surface area, and active functional groups of the resulting biochar and that the biochar produced at a charring temperature of 600 °C had the strongest adsorption capacity for Pb(II), which could reach 190.7 mg/g [45].
(2) Removal of heavy metals from water by modified biochar
Zhao Jie et al. used HNO3, H3PO4, NH3—H2O, and Ca(OH)2 to modify biochar at a carbonization temperature of 400 °C. The results of acid modification showed that the acidic functional group content in the HNO3—modified biochar and H3PO4—modified biochar increased and the pH of the acid—modified biochar decreased, and its corresponding pHpzc increased, while the results of the alkaline—modified biochar and the acid—modified biochar were diametrically opposed. The adsorption of Cr(VI) by acid—modified biochar was better than that by alkaline—modified biochar, and the best adsorption capacity of Cr(VI) by H3PO4 modified biochar was 101.82 mg/g, while that of unmodified biochar was 58.48 mg/g, indicating that the adsorption capacity of modified biochar for heavy metals was enhanced [46]. The Douglas fir biochar (DFBC) obtained by rapid charring at high temperatures was modified by KOH activation by Herath et al. The experimental results showed that the surface area of KOH—activated modified biochar (KOHBC) increased from 535 m2/g without modification to 1049 m2/g, and the adsorption capacities for heavy metals Pb(II), Cr(II), and Cd(II) were up to 140.0, 127.2 and 29.0 mg/g, respectively, at the optimum pH conditions for each heavy metal [47]. Qu et al. investigated the effect of KOH activation on the removal of Cr(VI) from water using corn straw as the raw material and biochar produced by a two—step carbonization process. The experimental results showed that KOH—activated modified carbon has a large specific surface area and many developed micropores, and its theoretical monolayer adsorption capacity for Cr(VI) can reach 116.97 mg/g, with the adsorption mechanisms mainly being electrostatic attraction, complexation, ion exchange and reduction [48].

6. Application of Biochar and Modified Biochar for Curing Heavy Metals in Soil

(1) Biochar solidification of heavy metals in soils
Biochar can fix heavy metals in contaminated substrates and soils because the products made from different biomass materials at suitable temperatures have a rich pore structure and are rich in surface functional groups such as carboxyl groups, hydroxyl groups, and amides. It can not only improve the fertility and permeability of the soil but also forms a coordination effect with a large number of heavy metal ions, effectively reducing the mobility of heavy metals in the substrate and soil and slowing down the toxic effects on plants [49].
Biochar is generally alkaline and can effectively raise the pH of the substrate and soil, which has a positive effect on the solidification of heavy metals contained in them. Its effectiveness in fixing heavy metals in contaminated substrates and soils is mainly influenced by the charring temperature and biomass [50]. A higher charring temperature usually increases the surface area and charring rate of biochar, which increases the adsorption capacity of pollutants and can reduce the bioavailability of heavy metals.
The specific surface area, porosity, and the number of functional groups of biochar from different sources also differed, which helped the biochar to solidify the heavy metals within it [51,52]. The experimental results showed that rice husk biochar could reduce the acid—soluble fraction of the contaminated sediment by 18–31%, while moso bamboo charcoal could reduce the acid—soluble fraction of Cu(II) by 79.71% [53,54].
Biochar not only has a fixation effect on heavy metals in contaminated substrates and soils but also reduces the heavy metal content in plants growing in contaminated soils. Gong et al. used tea—waste—derived biochar (TB) for the phytoremediation of Cd(II)—contaminated sediments. The results showed that TB at application rates of 100, 500, and 1000 mg/kg increased the accumulation and translocation of Cd(II) in ramie seedlings by altering the morphology of Cd(II) in the sediment and changing the subcellular distribution of Cd(II) in the plant cells. Low levels of TB reduced the toxicity of Cd(II) to ramie seedlings by promoting plant growth and alleviating oxidative stress. The results showed that a low concentration of biochar could improve phytoremediation efficiency and reduce the toxicity of Cd(II) to plants and microorganisms in the soil [55].
(2) Modified biochar to solidify heavy metals in soil
Zou Qi et al. used red mud—modified biochar to immobilize Cd(II) from the subsoil of the Xiangjiang River, and their results showed that red mud—modified biochar significantly reduced the concentration of As in soil (p < 0.05) [56]. The experimental results showed that the overlying water and pore water concentrations of Cd(II) decreased by 71% and 49%, respectively, after the activated biochar treatment, and the bioavailability of Cd(II) decreased, which proved that the specific surface area and oxygen—containing functional group content of activated biochar were related to the immobilization of Cd(II) in sediments [57].
The modification of biochar with different modifiers showed different inhibitory effects on the release of heavy metals from the bottom sediment. Cao Jing et al. prepared four different types of modified biochar with FeCl2, AICI3, MgCl2, and KMnO4 as modifiers and investigated their effects on controlling the release of heavy metal ions into water from two types of polluted substrates in urban river networks and lakes in Jiaxing City. The study showed that the remediation effect of adding AICI3—modified biochar was the best for Ni(II) > As contaminated sediment, and the concentrations of Ni(II) and As released into water from the two contaminated sediments could be reduced at most by 72.13% and 46.21%, respectively; the concentration of As released into water from the two contaminated sediments could be reduced at most by 95.80% after adding FeCb—modified biochar, but the concentration of Ni(II) in water increased. After adding FeCl2—modified biochar, the concentrations of Ni(II) and As pollutants released from the two contaminated substrates into the water increased [58].
Modified biochar not only has a remediation effect on the soil contaminated with heavy metals but also reduces the heavy metal content in plants growing in the contaminated soil. Sun Tong et al. studied the passivation and remediation of weakly alkaline Cd (II) contaminated soil by calcium—based modified biochar and its effects on soil physicochemical properties and Cd (II) accumulation in plants. The effective Cd(II) content of the soil was reduced by 12–30.2%, and the morphology of Cd(II) in the soil changed from the more active exchangeable and reducible states to the more stable residue state. The Cd content in the kernels of Zhengdan 958, Liyu 16, and Sanbei 218 was reduced by 52.65–72.56%, 37.54–50.80%, and 23.6–51.2%, respectively, compared with the control before the application of the modified activated carbon [59].

7. Conclusions

Adsorption is nowadays the most commonly used method for treating heavy metals in water, which has the advantages of being renewable, having low cost, having no “secondary pollution” and being suitable for treating wastewater of various concentrations. Biochar adsorbent has become a common material for treating heavy metals in wastewater because it is environmentally friendly, low—cost, and easy to obtain. Although biochar has a certain adsorption effect on heavy metals, the adsorption capacity is relatively limited. In order to improve the utilization of biochar, it is necessary to modify biochar to effectively enhance its remediation function further. In this paper, we have analyzed different modification methods of biochar from the adsorption mechanisms of biochar, compared the application of biochar before and after modification for heavy metal adsorption in both water and soil, and detailed the treatment effects and influencing factors of biochar before and after modification.
In the future, we can explore new biomass carbonization materials and rationalize the use of renewable waste resources to find more suitable adsorbents. Meanwhile, modified biochar materials will be further applied to the treatment of heavy metals in water and soil in a reasonable way. It is also worth noting that, in the future, the preparation of selective adsorbent materials can be considered through optimal modification, which can be more efficiently applied to the treatment of water and soil pollution in mixed systems in actual production and life. In addition, in the context of a green and environmentally friendly environment, we should pay more attention to the repeated recycling of waste biomass to ensure a good treatment effect without causing secondary pollution to the environment.

Author Contributions

Conceptualization, S.L. and H.L.; methodology, H.L. and Y.W.; validation, Y.W., H.L. and S.L.; formal analysis, Y.W.; resources, Y.W.; ing—review and editing, Y.W. All authors have reawriting—original draft preparation, Y.W.; writd and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Wang, J. Research progress of source and treatment methods of heavy metals in water. Guangdong Chem. Ind. 2014, 41, 87–88. [Google Scholar]
  2. Chen, G. Electrochemical technologies in wastewater treatment. Sep. Purif. Technol. 2004, 38, 11–41. [Google Scholar] [CrossRef]
  3. Yi, Y.; Yang, Z.; Zhang, S. Ecological risk assessment of heavy metals in sediment and human health risk assessment of heavy metals in fishes in the middle and lower reaches of the Yangtze River basin. Environ. Pollut. 2011, 159, 2575–2585. [Google Scholar] [CrossRef] [PubMed]
  4. Fang, J.; Xiong, Y.; Wu, F.; Wang, S.; Yang, H.; Xie, W.; Xie, Y. Composition and source identification of biomarkers in surface sediments from typical freshwater lakes in China. Environ. Pollut. Control 2017, 39, 822–828. [Google Scholar]
  5. Wang, T. The Effects of Additives on Adsorption of Heavy Metals onto Surficial Sediments. Master’s Thesis, Jilin University, Nanjing, China, 2008. [Google Scholar]
  6. Islam, M.S.; Ahmed, M.K.; Raknuzzaman, M.; Habibullah-Al-Mamun, M.; Islam, M.K. Heavy metal pollution in surface water and sediment: A preliminary assessment of an urban river in a developing country. Ecol. Indic. 2015, 48, 282–291. [Google Scholar] [CrossRef]
  7. Chang, T.C.; Yen, J.H. On-site mercury-contaminated soils remediation by using thermal desorption technology. J. Hazard. Mater. 2006, 128, 208–217. [Google Scholar] [CrossRef]
  8. Diao, Z.; Shi, T.; Wang, S.; Huang, X.; Zhang, T.; Tang, Y.; Zhang, X.; Qiu, R. Silane-based coatings on the pyrite for remediation of acid mine drainage. Water Res. 2013, 47, 4391–4402. [Google Scholar] [CrossRef]
  9. Wang, F.; Bao, K.; Huang, C.; Zhao, X.; Han, W.; Yin, Z. Adsorption and pH values determine the distribution of cadmium in terrestrial and marine soils in the Nansha area, Pearl River Delta. Int. J. Environ. Res. Public Health 2022, 19, 793. [Google Scholar] [CrossRef]
  10. GB/T 33422–2016; Thermoplastic Elastomer—Determination of Heavy Metal Contents—Inductively Coupled Plasma Atomic Emission Spectrometric Method. China National Standardization Administration Committee: Beijing, China, 2016.
  11. Mohan, D.; Sarswat, A.; Ok, Y.S.; Pittman, C.U. Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent—A critical review. Bioresour. Technol. 2014, 160, 191–202. [Google Scholar] [CrossRef]
  12. Singh, E.; Kumar, A.; Mishra, R.; You, S.; Singh, L.; Kumar, S.; Kumar, R. Pyrolysis of waste biomass and plastics for production of biochar and its use for removal of heavy metals from aqueous solution. Bioresour. Technol. 2021, 320, 124278. [Google Scholar] [CrossRef]
  13. Park, J.H.; Ok, Y.S.; Kim, S.H.; Cho, J.S.; Heo, J.S.; Delaune, R.D.; Seo, D.C. Competitive adsorption of heavy metals onto sesame straw biochar in aqueous solutions. Chemosphere 2016, 142, 77–83. [Google Scholar] [CrossRef] [PubMed]
  14. Prochaska, J.O.; DiClemente, C.C.; Norcross, J.C. In search of how people change: Applications to addictive behaviors. Am. Psychol. 1992, 47, 1102–1114. [Google Scholar] [CrossRef] [PubMed]
  15. Lin, X.Q.; Lü, Q.F.; Li, Q.; Wu, M.; Liu, R. Fabrication of low-cost and ecofriendly porous biocarbon using konjaku flour as the raw material for high-performance supercapacitor application. ACS Omega 2018, 3, 13283–13289. [Google Scholar] [CrossRef] [Green Version]
  16. Higashikawa, F.S.; Conz, R.F.; Colzato, M.; Cerri, C.E.P.; Alleoni, L.R.F. Effects of feedstock type and slow pyrolysis temperature in the production of biochars on the removal of cadmium and nickel from water. J. Clean. Prod. 2016, 137, 965–972. [Google Scholar] [CrossRef]
  17. Tan, X.; Liu, Y.; Zeng, G.; Wang, X.; Hu, X.; Gu, Y.; Yang, Z. Application of biochar for the removal of pollutants from aqueous solutions. Chemosphere 2015, 125, 70–85. [Google Scholar] [CrossRef] [PubMed]
  18. Inyang, M.I.; Gao, B.; Yao, Y.; Xue, Y.; Zimmerman, A.; Mosa, A.; Pullammanappallil, P.; Ok, Y.S.; Cao, X. A review of biochar as a low-cost adsorbent for aqueous heavy metal removal. Crit. Rev. Environ. Sci. Technol. 2016, 46, 406–433. [Google Scholar] [CrossRef]
  19. Beesley, L.; Moreno—Jiménez, E.; Gomez—Eyles, J.L. Effects of biochar and greenwaste compost amendments on mobility, bioavailability and toxicity of inorganic and organic contaminants in a multi-element polluted soil. Environ. Pollut. 2010, 158, 2282–2287. [Google Scholar] [CrossRef]
  20. Qian, L.; Zhang, W.; Yan, J.; Han, L.; Gao, W.; Liu, R.; Chen, M. Effective removal of heavy metal by biochar colloids under different pyrolysis temperatures. Bioresour. Technol. 2016, 206, 217–224. [Google Scholar] [CrossRef] [Green Version]
  21. Mukherjee, A.; Zimmerman, A.R.; Harris, W. Surface chemistry variations among a series of laboratory-produced biochars. Geoderma 2011, 163, 247–255. [Google Scholar] [CrossRef]
  22. Zhuang, C.; Yuan, L. Adsorption characteristics of modified biochar on Cr. J. Fudan 2021, 60, 779–788. [Google Scholar]
  23. Tong, X. Removal of Cu(II) from Aqueous Solutions and Its Fixation in Red Soil by Biochars from Crop Straws. Master’s Thesis, Nanjing Agricultural University, Nanjing, China, 2011. [Google Scholar]
  24. Dong, X.; Ma, L.; Zhu, Y.J.; Li, Y.C.; Gu, B.H. Mechanistic investigation of mercury sorption by Brazilian pepper biochars of different pyrolytic temperatures based on X-ray photoelectron spectroscopy and flow calorimetry. J. Environ. Sci. Technol. 2013, 47, 12156–12164. [Google Scholar] [CrossRef] [PubMed]
  25. Li, H.; Dong, X.; da Silva, E.B.; de Oliveira, L.M.; Chen, Y.; Ma, L.Q. Mechanisms of metal sorption by biochars: Biochar characteristics and modifications. Chemosphere 2017, 178, 466–478. [Google Scholar] [CrossRef] [PubMed]
  26. Li, A.Y.; Deng, H.; Jiang, Y.H.; Ye, C.H.; Yu, B.G.; Zhou, X.L.; Ma, A.Y. Superefficient removal of heavy metals from wastewater by Mg-loaded biochars: Adsorption characteristics and removal mechanisms. Langmuir 2020, 36, 9160–9174. [Google Scholar] [CrossRef]
  27. Alothman, Z.A.; Yilmaz, E.; Habila, M.; Soylak, M. Solid phase extraction of metal ions in environmental samples on 1-(2-pyridylazo)-2-naphthol impregnated activated carbon cloth. Ecotoxicol. Environ. Saf. 2015, 112, 74–79. [Google Scholar] [CrossRef] [PubMed]
  28. Kadirvelu, K.; Faur—Brasquet, C.; Le Cloirec, P. Removal of Cu(II), Pb(II), and Ni(II) by adsorption onto activated carbon cloths. J. Langmuir 2000, 16, 8404–8409. [Google Scholar] [CrossRef]
  29. Wang, F.; Shih, K.M.; Li, X.Y. The partition behavior of perfluorooctanesulfonate (PFOS) and perfluorooctanesulfonamide (FOSA) on microplastics. Chemosphere 2015, 119, 841–847. [Google Scholar] [CrossRef]
  30. Chen, J.Y.; Zhu, D.Q.; Sun, C. Effect of heavy metals on the sorption of hydrophobic organic compounds to wood charcoal. J. Environ. Sci. Technol. 2007, 41, 2536–2541. [Google Scholar] [CrossRef]
  31. Xu, X.; Cao, X.; Zhao, L. Comparison of rice husk- and dairy manure-derived biochars for simultaneously removing heavy metals from aqueous solutions: Role of mineral components in biochars. Chemosphere 2013, 92, 955–961. [Google Scholar] [CrossRef]
  32. Zama, E.F.; Zhu, Y.G.; Reid, B.J.; Sun, G.X. The role of biochar properties in influencing the sorption and desorption of Pb(II), Cd(II) and As(III) in aqueous solution. J. Clean. Prod. 2017, 148, 127–136. [Google Scholar] [CrossRef] [Green Version]
  33. Su, H.; Fang, Z.; Tsang, P.E.; Fang, J.; Zhao, D. Stabilisation of nanoscale zero-valent iron with biochar for enhanced transport and in-situ remediation of hexavalent chromium in soil. Environ. Pollut. 2016, 214, 94–100. [Google Scholar] [CrossRef]
  34. Ahmed, M.B.; Zhou, J.L.; Ngo, H.H.; Guo, W.; Chen, M. Progress in the preparation and application of modified biochar for improved contaminant removal from water and wastewater. Bioresour. Technol. 2016, 214, 836–851. [Google Scholar] [CrossRef] [PubMed]
  35. Yuan, P.; Wang, J.; Pan, Y.; Shen, B.; Wu, C. Review of biochar for the management of contaminated soil: Preparation, application and prospect. Sci. Total Environ. 2019, 659, 473–490. [Google Scholar] [CrossRef] [PubMed]
  36. Monser, L.; Adhoum, N. Modified activated carbon for the removal of copper, zinc, chromium and cyanide from wastewater. Sep. Purif. Technol. 2002, 26, 137–146. [Google Scholar] [CrossRef]
  37. Song, J.; Zhang, S.; Li, G.; Du, Q.; Yang, F. Preparation of montmorillonite modified biochar with various temperatures and their mechanism for Zn ion removal. J. Hazard. Mater. 2020, 391, 121692. [Google Scholar] [CrossRef] [PubMed]
  38. Manyà, J.J.; Ortigosa, M.A.; Laguarta, S.; Manso, J.A. Experimental study on the effect of pyrolysis pressure, peak temperature, and particle size on the potential stability of vine shoots-derived biochar. Fuel 2014, 133, 163–172. [Google Scholar] [CrossRef]
  39. Wang, J.; Wang, S. Preparation, modification and environmental application of biochar: A review. J. Clean. Prod. 2019, 227, 1002–1022. [Google Scholar] [CrossRef]
  40. Yin, R.; Guo, W.; Wang, H.; Du, J.; Wu, Q.; Chang, J.S.; Ren, N. Singlet oxygen-dominated peroxydisulfate activation by sludge-derived biochar for sulfamethoxazole degradation through a nonradical oxidation pathway: Performance and mechanism. Chem. Eng. J. 2019, 357, 589–599. [Google Scholar] [CrossRef]
  41. Hameed, B.H.; Din, A.T.M.; Ahmad, A.L. Adsorption of methylene blue onto bamboo-based activated carbon: Kinetics and equilibrium studies. J. Hazard. Mater. 2007, 141, 819–825. [Google Scholar] [CrossRef]
  42. Krasucka, P.; Pan, B.; Ok, Y.S.; Mohan, D.; Sarkar, B.; Oleszczuk, P. Engineered biochar—A sustainable solution for the removal of antibiotics from water. Chem. Eng. J. 2021, 405, 126926. [Google Scholar] [CrossRef]
  43. Das, S.K.; Ghosh, G.K.; Avasthe, R. Conversion of crop, weed and tree biomass into biochar for heavy metal removal and wastewater treatment. Biomass Convers. Biorefinery 2021, 1–4. [Google Scholar] [CrossRef]
  44. Jia, Y.; Shi, S.; Liu, J. Study of the effect of pyrolysis temperature on the Cd2+ adsorption characteristics of biochar. Appl. Sci. 2018, 8, 1019–1032. [Google Scholar] [CrossRef] [Green Version]
  45. Xiao, Y.; Xue, Y.; Gao, F.; Mosa, A. Sorption of heavy metal ions onto crayfish shell biochar: Effect of pyrolysis temperature, pH and ionic strength. J. Taiwan Inst. Chem. Eng. 2017, 80, 114–121. [Google Scholar] [CrossRef]
  46. Zhao, J.; He, Y.; Zhang, X.; Li, Q.; Yang, W. Effect on Cr(VI) adsorption performance of acid-base modified biochar. Environ. Eng. 2020, 38, 28–34. [Google Scholar]
  47. Herath, A.; Layne, C.A.; Perez, F.; Hassan, E.I.B.; Pittman, C.U.; Mlsna, T.E. KOH-activated high surface area Douglas Fir biochar for adsorbing aqueous Cr(VI), Pb(II) and Cd(II). Chemosphere 2021, 269, 128409. [Google Scholar] [CrossRef] [PubMed]
  48. Qu, J.; Wang, Y.; Tian, X.; Jiang, Z.; Deng, F.; Tao, Y.; Jiang, Q.; Wang, L.; Zhang, Y. KOH-activated porous biochar with high specific surface area for adsorptive removal of chromium (VI) and naphthalene from water: Affecting factors, mechanisms and reusability exploration. J. Hazard. Mater. 2021, 401, 123292. [Google Scholar] [CrossRef]
  49. Zhang, Y.; Zhang, Y.; Akakuru, O.U.; Xu, X.; Wu, A. Research progress and mechanism of nanomaterials-mediated in-situ remediation of cadmium-contaminated soil: A critical review. J. Environ. Sci. 2021, 104, 351–364. [Google Scholar] [CrossRef]
  50. Bian, R.; Chen, D.; Liu, X.; Cui, L.; Li, L.; Pan, G.; Xie, D.; Zheng, J.; Zhang, X.; Zheng, J.; et al. Biochar soil amendment as a solution to prevent Cd-tainted rice from China: Results from a cross-site field experiment. Ecol. Eng. 2013, 58, 378–383. [Google Scholar] [CrossRef]
  51. Zhao, W.; Bi, X.; Peng, Y.; Bai, M. Research advances of the phosphorus-accumulating organisms of Candidatus Accumulibacter, Dechloromonas and Tetrasphaera: Metabolic mechanisms, applications and influencing factors. Chemosphere 2022, 307, 135675. [Google Scholar] [CrossRef]
  52. Tang, J.; Zhu, W.; Kookana, R.; Katayama, A. Characteristics of biochar and its application in remediation of contaminated soil. J. Biosci. Bioeng. 2013, 116, 653–659. [Google Scholar] [CrossRef]
  53. Que, W.; Zhou, Y.H.; Liu, Y.G.; Wen, J.; Tan, X.F.; Liu, S.J.; Jiang, L.H. Appraising the effect of in-situ remediation of heavy metal contaminated sediment by biochar and activated carbon on Cu immobilization and microbial community. Ecol. Eng. 2019, 127, 519–526. [Google Scholar] [CrossRef]
  54. Zhang, C.; Shan, B.; Zhu, Y.; Tang, W. Remediation effectiveness of Phyllostachys pubescens biochar in reducing the bioavailability and bioaccumulation of metals in sediments. Environ. Pollut. 2018, 242, 1768–1776. [Google Scholar] [CrossRef]
  55. Gong, X.; Huang, D.; Liu, Y.; Zeng, G.; Chen, S.; Wang, R.; Xu, P.; Cheng, M.; Zhang, C.; Xue, W. Biochar facilitated the phytoremediation of cadmium contaminated sediments: Metal behavior, plant toxicity, and microbial activity. Sci. Total Environ. 2019, 666, 1126–1133. [Google Scholar] [CrossRef] [PubMed]
  56. Zou, Q.; An, W.; Wu, C.; Li, W.; Fu, A.; Xiao, R.; Chen, H.; Xue, S. Red mud-modified biochar reduces soil arsenic availability and changes bacterial composition. Environ. Chem. Lett. 2018, 16, 615–622. [Google Scholar] [CrossRef]
  57. Liu, S.J.; Liu, Y.G.; Tan, X.F.; Zeng, G.M.; Zhou, Y.H.; Liu, S.B.; Yin, Z.H.; Jiang, L.H.; Li, M.F.; Wen, J. The effect of several activated biochars on Cd immobilization and microbial community composition during in-situ remediation of heavy metal contaminated sediment. Chemosphere 2018, 208, 655–664. [Google Scholar] [CrossRef] [PubMed]
  58. Liu, Q.; Sheng, Y.; Wang, W.; Li, C.; Zhao, G. Remediation and its biological responses of Cd contaminated sediments using biochar and minerals with nanoscale zero-valent iron loading. Sci. Total Environ. 2020, 713, 136650. [Google Scholar] [CrossRef]
  59. Sun, T.; Li, K.; Fu, Y.; Ma, W.; Xie, X.; Sun, Y. Effect of modified biochar on immobilization remediation of weakly alkaline Cd-contaminated soil and environmental quality. Acta Sci. Circumst. 2020, 40, 2571–2580. [Google Scholar]
Water 14 03894 g001 550
Figure 1. Adsorption mechanism of biochar.
Figure 1. Adsorption mechanism of biochar.
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Figure 2. Schematic diagram of the surface microstructure of biochar.
Figure 2. Schematic diagram of the surface microstructure of biochar.
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Figure 3. Schematic diagram of the behavior of biochar.
Figure 3. Schematic diagram of the behavior of biochar.
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Table
Table 1. Adsorption mechanism of heavy metals by biochar and modified biochar.
Table 1. Adsorption mechanism of heavy metals by biochar and modified biochar.
MechanismPrincipleMain Influencing FactorsReferences
Surface
absorption		The surface of biochar is rich in acidic groups such as carboxyl groups and phenolic hydroxyl groups, which can form specific metal complexes with heavy metal ions in water/soil and form active adsorption sites, etc.1. Surface chemical bond group
2. Diffusion effect of heavy metal ions
3. Temperature		[17,18,19,20]
Electrostatic
Adherence		Formation of ionic bonds (formed when atoms gain or lose electrons) between anions and cations by electrostatic interaction (chemical bonding).1. Zeta potential
2. pH value.
3. Degree of dispersion		[21,22,23]
Ion ExchangeThe charged cations and protons on the surface of biochar exchange with dissolved heavy metal ions in an exchange reaction.1.Nature of the surface functional groups
2. Size of the pollutants
3. Live nature
4. pH value		[24,25]
Chemical
Precipitation		Anions react with heavy metal ions to form a water—insoluble precipitate.1. pH value.
2. Electrolyte concentration
3. Complexing effect
4. Homonymous ion effect		[29,30,31,32]
Table
Table 2. Modification methods and principles of modified biochar.
Table 2. Modification methods and principles of modified biochar.
Modification MethodModified MaterialsModification PrincipleReferences
Physical modificationCO2, H2O, AirBy reacting the gas with the biochar at high temperatures, the pores of the biochar are increased, and its specific surface area is expanded.[34]
Redox modificationFeCl3, MnSO4, CO2, NH3Using oxidizing and reducing agents to carry out redox reactions on the functional groups on the surface of biochar to increase the surface active matching point.[35]
Acid–base
surface modification		CO2, NH3, KOH, NaOHUsing acid and alkali treatment of raw materials or direct treatment of biochar to change the acid and alkali functional groups on the surface of the biochar.[36]
Adsorbent
compound modification		Nanocomposites such as chitosanNanocomposites such as chitosan are rich in amino—functional groups with strong binding capacity and thus can be used as adsorption sites for heavy metals.[37,38]
Activation modificationKOH, NaOH, ZnCl2, H3PO4The activator reacts with the functional groups on the surface of the biochar at high temperatures and introduces a large number of active sites, increasing the number of pores on the surface of the biochar and increasing the diameter of the pores.[39,40]
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Wang, Y.; Li, H.; Lin, S. Advances in the Study of Heavy Metal Adsorption from Water and Soil by Modified Biochar. Water 2022, 14, 3894. https://doi.org/10.3390/w14233894

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Wang Y, Li H, Lin S. Advances in the Study of Heavy Metal Adsorption from Water and Soil by Modified Biochar. Water. 2022; 14(23):3894. https://doi.org/10.3390/w14233894

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Wang, Yizhuo, He Li, and Shaohua Lin. 2022. "Advances in the Study of Heavy Metal Adsorption from Water and Soil by Modified Biochar" Water 14, no. 23: 3894. https://doi.org/10.3390/w14233894

APA Style

Wang, Y., Li, H., & Lin, S. (2022). Advances in the Study of Heavy Metal Adsorption from Water and Soil by Modified Biochar. Water, 14(23), 3894. https://doi.org/10.3390/w14233894

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