Characteristics and Applications of Sewage Sludge Biochar Modified by Ferrous Sulfate for Remediating Cr(VI)-Contaminated Soils

Table 5

RAC criteria.

Grade	Exchangeable fraction content	Risk
I	<1	No risk
II	1–10	Low risk
III	11–30	Medium risk
IV	30–50	High risk
V	50	Very risk