The main parameters obtained for the studied samples are
listed in Table 1. In general, the samples were alkaline except for
materials derived from the oil extraction processes (OP and
OWH). The LOI and TOC values indicated that the organic matter
content of the biochars and materials derived from the oil industry
was over 90%, but composts and especially the green material had
much lower organic matter content. For all of the samples, the C
content was close to the TOC values with the exception of the
GW material, which is due to the presence of carbonate phases.
The samples showed high CEC values, which was consistent with
their high organic matter content. However, the two variables were
not correlated, which is most likely due to the different nature of
the organic matter in the examined materials.