# Effects of Manure Waste Biochars in Mining Soils
## Results
### Characterization of Amended Mining Soils: Trace Metal Mobility
The effect of biochars in the soil pH in the Mijarojos-Cantabria area was different in the three soils (M1, M2, M3). Initial pH values of soils M1, M2, and M3 were alkaline. There was no significant effect on the pH of M1 soil (pH: 7.91) after biochar addition. In M2 (pH: 8.23), there was an increase in soil pH, while for M3, a liming effect was found only for some biochars. There was a significant increase in electrical conductivity (EC) after biochar addition in the three areas (Tables 4-6). For the Zarandas-Andalusia area (Table 4), the EC of the three soils (EC: 0.09-0.24 dS-m\({}^{-1}\)) increased to values between 1.61 and 3.61 dS-m\({}^{-1}\); for the Portman-Murcia area (Table 5), the EC of the four soils (EC: 0.37-3.10 dS-m\({}^{-1}\)) increased to values between 1.46 and 5.41 dS-m\({}^{-1}\). Finally, for the Mijarojos-Cantabria area, EC increased more than 170 times for soil M1, 330 times for M2 soil, and 105 times for soil M3 from an initial EC lower than 1 dS-m\({}^{-1}\). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **EC** & **Cr** & **Cu** & **Ni** & **Fe** & **Zn** & **Cd** & **Pb** \\ \cline{2-10}  & **pH** & **dS-m\({}^{-1}\)** & **mg-kg\({}^{-1}\)** & **kg-kg\({}^{-1}\)** & **mg-kg\({}^{-1}\)** & \\ \hline
**Z1** & 5.81a & 0.16a & 0.56b & 0.41b & 6.10c & 5.22d & 1.46b & 0.07a & 6.894 \\
**Z1** + **BPL450** & 8.44d & 2.23c & 0.35a & 0.50c & 3.81a & 1.84a & 0.32a & 0.07a & 2.78a \\
**Z1** + **BPL450** & 8.46d & 2.24c & 0.31a & 0.65d & 3.74a & 3.48c & 0.32a & 0.06b & 2.28 ab \\
**Z1** + **BRM450** & 8.07b & 1.61b & 0.73c & 0.61d & 3.98 ab & 2.61b & 0.28a & 0.06b & 3.61c \\
**Z1** + **BRM600** & 8.21c & 1.65b & 0.70c & 0.15a & 4.66b & 2.15 ab & 0.28a & 0.07a & 4.17c \\ \hline
**Z2** & 5.10a & 0.09a & 1.07d & 0.54b & 0.54c & 6.84d & 1.37c & 0.07a & 6.35c \\
**Z2** + **BPL450** & 9.43e & 2.25c & 0.23a & 0.21a & 0.29a & 3.10c & 0.13a & 0.06b & 5.93b \\
**Z2** + **BPL600** & 9.18d & 2.50d & 0.70c & 0.18a & 0.40d & 0.19b & 0.28a & 0.06b & 5.38b \\
**Z2** + **BRM450** & 7.73b & 2.05b & 0.50b & 0.24a & 0.29a & 2.16 ab & 0.16a & 0.05b & 3.75a \\
**Z2** + **BMR450** & 7.97c & 2.25c & 1.08d & 0.21a & 0.34a & 2.70c & 0.18a & 0.06b & 4.08a \\ \hline
**Z3** & 3.86a & 1.24a & 1.51d & 0.48b & 0.17e & 0.54a & 0.72d & 0.07a & 5.254 \\
**Z3** + **BPL450** & 7.29b & 3.49e & 0.78b & 0.15a & 0.46b & 0.34b & 0.22b & 0.05b & 3.57a \\
**Z3** + **BPL600** & 7.66c & 3.61c & 0.64a & 0.18a & 0.63c & 0.31b & 0.14a & 0.05b & 4.80c \\
**Z3** + **BMR450** & 8.13d & 2.94b & 0.79b & 0.11a & 0.01a & 0.01d & 0.04c & 0.06b & 4.11 ab \\
**Z3** + **BMR600** & 8.08e & 2.75b & 1.20c & 0.15a & 0.85d & 0.35b & 0.43c & 0.06b & 4.33 bc \\ \hline \hline \end{tabular} \({}^{1}\) Values in different columns followed by the same letter are not significantly different (\(p=0.05\)) using the Duncan test for each soil with their amendments.  
\end{table} 
Table 4: pH, Electrical conductivity (EC), and mobile metal content in control soils and biochar/soil mixtures from Zarandas area after 180 incubation days. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **EC** & **Cr** & **Cu** & **Ni** & **Fe** & **Zn** & **Cd** & **Pb** \\ \cline{2-10}  & **pH** & **dS-m\({}^{-1}\)** & **mg-kg\({}^{-1}\)** & **kg-kg\({}^{-1}\)** & **mg-kg\({}^{-1}\)** & \\ \hline
**P1** & 8.42a \({}^{1}\) & 0.37a & 0.24a & 0.38a & 1.22d & 11.69b & 0.21a & 0.83a & 14.24b \\
**P1** + **BPL450** & 8.63b & 2.21c & 0.11a & 0.38a & 1.67e & 15.46c & 0.25a & \(<\)0.01b &  
The application of all biochars reduced, in general, the mobility of trace metals in the three soils (Z1, Z2, and Z3) of the Zarandas-Andalusia area (Table 4). For the Z1 soil, the four biochars reduced the mobility of Ni (24-39%), Zn (78-81%), Cd (14%), and Pb (39-67%). However, this was not always the case for Cu and Cr. In addition, the four biochars reduced the percentage of trace metal mobility in both Z2 and Z3 soils.