Heavy metal in three different concentrations of soaking solutions descended gradually with removal rate and absorptive capacity rising. After 7 days, 100 mg/L and 150 mg/L Zn solution reached approximately 0 mg/L with removal rate of 95%, whereas 300 mg/L took 17 days for reaching 0 mg/L. After 17 days, the concentration of Cu in the former 100 mg/L, 150 mg/L, and 300 mg/L solution reached approximately zero with a removal rate of 95%. After reaching adsorption equilibrium, heavy metal concentration started to rise at 27th day. Concentration variation of three different Pb solutions was consistent and reached 0 mg/L and a removal rate of 95%. After 17 days, 100 mg/L and 150 mg/L Cd solution reached approximately 0 mg/L with removal rate of 95%, whereas 300 mg/L took 27 days for reaching 0 mg/L. Variation of Cr showed a similar pattern with Zn. After 7 days, 100 mg/L and 150 mg/L Cr solution reached approximately 0 mg/L with a removal rate of 95%, whereas 300 mg/L took 17 days for reaching 0 mg/L.

Absorption pattern of Cu solution on C&D waste was different from the other two metals. Variation trends of 100 and 150 mg/L of Cu in mixed heavy metal solution had a similar pattern. Adsorption rate was fast on the first day and then slowed down. Removal rate of 150 mg/L reached the maximum value on the seventh day. The 150 mg/L Cu solution reached adsorption equilibrium on the 17th day. The 300 mg/L Cu mixed solution obtained the maximum adsorption capacity after 2 days and started descended on the fifth day then reached equilibrium. When the absorption process came to the end, the 300 mg/L solution obtained maximum adsorptive capacity of Cu, whereas the 150 mg/L solution obtained the minimum value. The 100 mg/L solution reached the maximum removal rate of Cu, whereas the 300 mg/L reached the minimum value.

Concentration of heavy metals in mixed solution in the first day varied in a similar way as pH which was due to the relatively higher acid in the solution and hydroxide precipitate could not be formed immediately. The concentration of Zn, Cu, Pb, Cd, and Cr concentration at day 10 were 0.047, 0.159, 0.315, <0.002 (less than detection limit), and 0.0519 mg/L, respectively.

Concentration of heavy metals in concrete is demonstrated in Fig. 5.13, where (A)–(E) are distribution of Zn, Cu, Pb, Cd, and Cr under single contamination and (F) is distribution of Zn, Cu, Pb, Cd, and Cr under multiple contamination. Results showed that Zn, Cu, Pb, and Cr existed in different depths under both single and multiple contaminations, whereas Cd could not be detected below 1 cm.

It was indicated in (A)–(E) from Fig. 5.13 that heavy metals were mainly concentrated within 1 cm below the surface. Alkaline substances might be released that resulted in the concentration and fixation of heavy metals on the surface. The concentration of Cu in the depth of 2.0–2.5 cm was higher than the background value. It was proved that Cu had a higher tendency of migration in the concrete than other heavy metals. Cd had the lowest migration capacity as it was found only in the depth of 0.5–1.0 cm.

Distribution of Zn, Cu, Pb, Cd, and Cr in the depth of 0–0.5 cm under multiple contaminations was similar in pattern, and the concentration was 1057, 1220.5, 1154, 1296.6, and 1220.4 mg/kg, respectively, all of which were lower than those under single contamination. However, in the depth of 0.5–1.0 cm, the concentration of heavy metals under multiple contamination were higher than those under single contamination, which might be due to the increase of penetration capacity of heavy metals resulted from the higher amount of ions. Little heavy metals existed below 1 cm except Cr, the concentration of which was higher than the background value in the depth of 1.5–2.0 cm, 2.0–2.5 cm, and 3.0–4.0 cm and was also higher than that under single contamination. Therefore the penetration capacity of Cr increased under multiple contaminations.

Mercury contents of three kinds of particle size (α, β, and γ) of the cement block, foam concrete, red brick, recycled aggregates from Dujiangyan, and regeneration sandstone from Pudong were measured after 5 days' mercury adsorption, indicating that the smaller the particle size was, the bigger adsorption capacity would be obtained. Mercury contents of the foam concrete α, β, and γ were measured as 83.66, 102.57, and 102.60 μg/kg, respectively, after 5 days' mercury adsorption, and the difference between the adsorption quantity of β and γ was very small; mercury content of the red brick α, β, and γ were measured as 15.41, 33.81, and 497.22 μg/kg, respectively, after 5 days' mercury adsorption, and adsorption capacity of γ was much higher than β and α. Mercury levels increased after 10 and 20 days' adsorption, but rate of increase was very small. The mercury levels of red brick β and α were still very low after 10 and 20 days' adsorption.

Mercury contents of the cement block α, β, and γ were measured as 50.04, 173.77, and 168.14 μg/kg after 150 days respectively. Adsorption capacity of the three was 40, 160, and 158 μg/kg respectively compared with background mercury content (10 μg/kg). The reason why adsorption quantity of β was only slightly larger than γ might be that the adsorption quantity of the two had reached a saturation level. It could be inferred that cement brick powder below 100 mesh would be contaminated after 150 days; mercury contents of three particle size of foam concrete samples were measured, and adsorption capacity of the particle size (α, β, and γ) were 172, 194, and 240 μg/kg, respectively, compared with background mercury content (80 μg/kg). Difference among adsorption quantity of the three was very small, and overall the smaller the particle size was, the bigger adsorption capacity would be obtained; mercury levels of red brick α, β, and γ was were measured and adsorption capacity of β or α was still much lower than γ. Adsorption capacity of the three were 83, 128, and 1112 μg/kg, respectively, compared with background mercury content (12 μg/kg). It can be inferred that red brick powder below 200 mesh were vulnerable to be contaminated; mercury content of three particle size of recycled aggregates from Dujiangyan were measured after 150 days, and adsorption capacity of the three were 172, 194, and 240 μg/kg, respectively, compared with background mercury content (15 μg/kg). Difference among adsorption quantity of the three was very small, indicating that different particle sizes had little effect on mercury adsorption for recycled aggregates; mercury contents of regeneration sandstone (α, β, and γ) from Pudong was measured as 88.13, 318.75, and 629.12 μg/kg, respectively, after 150 days. Adsorption capacity of the three were 68, 299, and 609 μg/kg, respectively, compared with background mercury content (20 μg/kg), indicating that the smaller the particle size was, the bigger adsorption capacity was, and mercury content of γ was nearly 2 times β and 10 times α.

Mercury content of five kinds of building materials were compared after 150 days' mercury adsorption as given in Fig. 5.15B, indicating that small particle contributed to a large mercury adsorption, however, different performance was found among various materials. The largest mercury content of α was the foam concrete content, the largest mercury content of β was the regeneration sandstone from Pudong, and the largest mercury content of γ was red brick. Compared with several other materials of γ, mercury content of red brick was 6.7 times that of the cement block, 3.5 times that of the foam concrete, 5.7 times that of the recycled aggregates from Dujiangyan, and 1.8 times that of the regeneration sandstone from Pudong, indicating that red brick was the most vulnerable building material to mercury contamination. Compared with secondary standard threshold of GB15168-1995 (300 μg/kg), the regeneration sandstone from Pudong of β went over the threshold, as well as the foam concrete, red brick, and regeneration sandstone from Pudong of γ after 150 days' mercury adsorption. Buildings will produce C&D waste powder in the process of demolition and reconstruction, of which foam concrete, red brick, and sand may be polluted by mercury.

Furthermore, mercury adsorption quantity of standard concrete block was up to 174.79 μg/kg within the limits of 1.0–1.5 cm and to 55.02 μg/kg within the limits of 1.5–2.0 cm, indicating that mercury pollution mainly focused on the limits of 1.0–1.5 cm, which was much higher than the initial content (39 ± 12 μg/kg). As a result, for some seriously mercury polluted factories and workshops, mercury pollution could be removed by peeling the skin of the concrete blocks before demolition and renovation process after full utilization.

XRD and XRF analysis of cement block, foam concrete, red brick, regeneration sandstone, and recycled aggregates, respectively, showed that five kinds of building materials were given priority to silicon dioxide, followed by calcium carbonate. SEM microscopic analysis on surfaces of five kinds of building material showed that the porosity of cement block and recycled aggregates was greater than that of the red brick, recycled sand, and foam concrete. Results showed that small particle contributed to large mercury adsorption, however, different performance was found among various materials.

Fig. 5.17 is the SEM photos of heavy metals/organic pollutants contaminated C&D waste. Among which (A) and (A) were 5000x and 20,000x photos of heavy metal contaminated C&D waste whereas (B) and (D) were 5000x and 20,000x photos of organic pollutants contaminated C&D waste. According to the photos, large damage in the morphology was found in heavy metal contaminated C&D waste. There were many loose pores on the surface of C&D waste and the waste particles were wrapped by crystal substances, which might be the hydroxides and oxides of heavy metals. The damage in morphology was not so evident in organic pollutant contaminated C&D waste. The waste was not significantly eroded and was wrapped in a layer of cotton-like substances.

Samples were crushed into particulates and powders from clean C&D waste was dried at 105°C for 12 h before use. The heavy metal contaminated C&D waste was simulated by soaking in metal solution of a certain concentration for 2 days and was dried at 80°C for 12 h before use.

Granular or powder samples (5 g) were weighed and placed in a batch of 100 mL brown bottles. A solution of 25 mL deionized water, 5 mL phorate, or 5 mL diethyl dithiophosphate was added into the bottle and sealed. Bottles were placed in a shaker and shaked at 25 ± 2°C for several hours with the rotation speed of 150 rpm. The supernatant was centrifuged at 1000 rpm for 1 min and extracted three times using hexane (5, 3, 2 mL) after being filtered through the PTFE membrane. Reconduct the steps above twice using and blank as a reference. The equation of equilibrium adsorption of organic pollutants on C&D waste was q_e = (C₀−C_e)V/W.

It was found that the pH value of solution with gypsum and brick powder was weak acid in which pH adjustment was not necessary. The other C&D waste would make the pH into strong alkaline in solution. Large interference would be caused in absorption experiments as metals would become hydroxide precipitate in this environment, while the too much acid for pH adjustment would make it hard to determine the volume. Therefore brick powder was used as the research subject as it was more common in industrial C&D waste.

Effects of the amount of C&D waste on adsorption of Pb (II), Zn (II), Cu (II), Cd (II), and Cr (III) is also introduced in this section. When the amount of C&D waste increased, the total heavy metal adsorption would no doubt. With the amount increased from 0.5 to 3.5 g, the absorption capacity of all heavy metals per gram decreased except Cr (III), in which the absorption capacity of Pb decreased most (from 2.4 to 0.7 mg/g). It was possibly due to the strength of the mutual reaction among C&D waste powder or particles with the increase of the amount of waste. The contact time and area between the waste and heavy metals would be reduced, which ultimately resulted in the decrease of absorption capacity.

Effects of the contact time on adsorption of Pb (II), Zn (II), Cu (II), Cd (II), and Cr (III) is reflected in this section. It was found that the absorption of five heavy metals was fast as the maximum absorption capacity was obtained 20 min later while the adsorption equilibrium was reached at around 30 min.

Adsorption of organic pollutants was investigated, the same adsorption capacity was also calculated using subtraction. As can be seen from the figure, the adsorption equilibration of diethyl dithiophosphate was obtained at about 120 min, while the highest adsorption capacity was 251 μg/g. The adsorption of triethyl phosphorothioate was largely influenced by the particle sizes, and the adsorption equilibration was also obtained at about 120 min. The absorption capacity of phorate was 90 μg/g, smaller than the other two organic pollutants, and no significant relationship with time was found. The absorption capacity of particulate C&D waste was larger than waste in powder, which was different with most absorbates.