**5. Conclusion**

*Advanced Sorption Process Applications*

The herbicide sorbed by the soil particles usually returns to the soil solution, that is, it is desorbed to be available again to the transport by absorption and degradation; however, this process in soils with biochar was less studied when compared

In contrast to sorption, desorption decreases when biochar is added to the soil and the herbicide eventually returns to the soil solution, and sorption can often become irreversible. Irreversible sorption of herbicides was reported by Yu et al. [61], Wang et al. [28], and Sopeña et al. [45], which included sorption of the herbicides in the specific surface area, trapped in micropores, and partitioned into condensed structures of the biochar particles. In a study with wheat straw at 1%

), Tatarková et al. [39] found the reduction of MCPA sorption from 64.2%

The reduction in herbicide desorption and consequently the lower concentration of these in the soil solution is more evident in altered soil with biochar in relation to the soil amended with the material. In this sense, there is, in general, a lower leaching potential of the herbicides and lower bioavailabilities of these, both for the

Another important factor in the properties of biochar is the action of time, which can alter the interaction of biochar with herbicides. Some physical processes such as breaking of the structure of biochar by the action of the climate can increase the specific surface area of the biochars [62] and the sorptive capacity of these materials. Kumari et al. [63] obtained higher specific surface area and cation exchange capacity (CEC) in soils amended with wood biochar (500°C) after 7–19 months, resulting in increased sorption of glyphosate in all soils of the study. Trigo et al. [64] observed an increase in the sorption of metolachlor in soils amended with distinct biochars over the years (macadamia: fresh = 2.4 times, 1 year = 2.5 times, 4 years = 1.9 times, wood: fresh = 2 times, and 5 years = 14 times). Martin et al. [38] evaluated sorption of atrazine and diuron in soil aged

biochar, there was an increase of twofold to fivefold in sorption of the herbicides in relation to the soil without biochar. With 5 years of aging, the biochar presented, in experiment with biochar of residues of the production of mushrooms and rice husk (70%) and peels of cotton seeds (30%) (400°C), increases in specific surface area of 98–114.3% according to Dong et al. [65]. However, the average pore diameter decreased and the surface was more propitious for material leaching. Structurally,

On the other hand, in some studies, the aging of the biochar particles in the soil resulted in the reduction in the sorption capacity of the herbicides by reducing the specific surface area and the porosity of the biochar as the material aging, blocking

) for 32 months. In this study, with fresh soil amended with

in unamended soil to 55.1% in biochar amended soil. For Loganathan et al. [41], the amount of atrazine remaining in sandy and clayey soils amended with biochar was higher than in unamended soils. Cabrera et al. [35] found the almost negligible desorption for aminocyclopyrachlor in biochar amended soil from wood pallets (>500°C). Wang et al. [28] also reported slower and lower desorption rates for terbuthylazine in soil amended with sawdust biochar produced at 700°C, followed by biochar produced at 350°C. On the other hand, Khorram et al. [4] have reported easier desorption of fomesafen molecules weakly bound to rice bark biochar

because the specific surface areas of the material are relatively low.

**4. Effect of biochar aged on herbicide sorption in soil**

**3.2 Desorption herbicides**

to the sorption process [23].

degradation and the control of weeds.

with biochar (10 t ha<sup>−</sup><sup>1</sup>

there was no difference in fresh material.

(m m<sup>−</sup><sup>1</sup>

**96**

The application of biochar in the remediation of soil contaminant herbicides is an interesting management alternative due to high sorption and low desorption with these chemicals. Although the use is well explored worldwide, there is still a need for further research because of contradictory results regarding the benefits of using biochar and its effects on production, plant protection, and environmental contaminants. In addition to verifying the different interactions of the biochar and its properties in agricultural soils, it is worth emphasizing the importance of the possibility of using different materials in the production of biochars derived from different agricultural and industrial activities, which can promote the rational use of resources and destine them to agricultural production and minimization of the environmental impacts caused by these activities.

## **Acknowledgements**

The authors would like to thank the São Paulo Research Foundation (FAPESP) process 2016/17683-1, for the financial support.

*Advanced Sorption Process Applications*
