*2.5. Statistical Analysis*

The metal sorption batch experiments were performed in triplicate and the soil sorption experiments were performed in six replicates. The data are presented as the mean values with the relative standard deviation (RSD). Student's *t*-tests were used to test for significant differences in cobalt fractions between biochar treated and untreated soils (*p* < 0.05). The obtained data were compiled using Microsoft Excel 2016 and Statistica Statsoft 13.3.

## **3. Results**
