Effects of remediation train sequence on decontamination of heavy metal-contaminated soil containing mercury

Figures & data

Table 1. Characteristics of study soil

Property	Value
Sand (%)	36
Silt (%)	20
Clay (%)	44
pH	8.2
Organic carbon (%)	1.3
CEC (cmol/kg)	14
CaCO3 equivalent (%)	4.98
DCB-extractable Fe (g/kg)	1.56
DCB-extractable Mn (g/kg)	0.35
Total Cr (mg/kg)	1600
Total Cu (mg/kg)	2270
Total Ni (mg/kg)	878
Total Pb (mg/kg)	2100
Total Zn (mg/kg)	999
Total Hg (mg/kg)	180

Table 2. Chemical fractions of Cr, Cu, Ni, Pb, and Zn in the initial soil

	F1 (mg/kg)	F2 (mg/kg)	F3 (mg/kg)	F4 (mg/kg)	F5 (mg/kg)	Sum (mg/kg)	Recovery (%)
Cr	0.30 ± 0.0	44.3 ± 5.7	620 ± 6.0	10.0 ± 0.7	789 ± 13	1460	89.9
Cu	1.10 ± 0.1	655 ± 84	1430 ± 29	146 ± 1.0	122 ± 4.5	2350	104
Ni	0.70 ± 0.1	55.0 ± 2.0	423 ± 0.1	13.6 ± 1.4	312 ± 2.5	804	91.7
Pb	3.50 ± 0.3	387 ± 40	1250 ± 1.6	45.4 ± 2.1	273 ± 6.4	1960	93.4
Zn	1.40 ± 0.0	192 ± 32	17.8 ± 0.4	54.3 ± 2.3	663 ± 16	929	93.0

Note: Recovery was obtained by sum of metal content in each fraction divided by the metal total content (F1: exchangeable, F2: bound to carbonate, F3: bound to Fe/Mn oxides, F4: bound to organic matter, and F5: residual).

Table 3. Chemical fractions (mg/kg) of Hg in the initial soil

F1	F2	F3	F4	Sum	Recovery (%)
0.05 ± 0.0	7.21 ± 1.0	0.20 ± 0.1	189 ± 13	196	109

Note: Recovery was obtained by sum of Hg content in each fraction divided by the Hg total content (F1: water soluble, F2: exchangeable, F3: bound to organic matter, and F4: residual).

Figure 1. Removal of heavy metals with HCl, CaCl₂, and EDTA at various concentrations.

Figure 2. Thermogravimetric analysis during heating at 5°C/min and 10°C/min.

Figure 3. Hg removal under single and remediation treatments: (A) chemical extraction, (B) thermal treatment, (C) chemical extraction followed by thermal treatment, and (D) thermal treatment followed by chemical extraction.

Figure 4. Heavy metals in soil extractable with 0.2 M EDTA before and after 550°C treatments.