Chapter Eight

Recycling Technologies and Pollution Potential for Contaminated Construction and Demolition Waste in Recycling Processes

Abstract

The most severely contaminated construction and demolition (C&D) waste is used as raw materials to produce recycled concrete blocks to test the leaching toxicity in the recycling process. The pollution potential for aggregate produced by Zn and As contaminated waste is high. Leaching amount of recycled concrete produced by demolition waste in Cr workshops from the electroplating factory is 154.31 mg/L and should be treated properly before recycling. Normal recycled concrete, normal recycled concrete blocks with coir fiber, and alkali-treated recycled concrete blocks with coir fiber have been produced using contaminated C&D waste, in which Cd shows the highest leaching potentials. The pollution potential for recycled materials after treatment by coir fiber or alkali is lower than others. Recycling of industrial construction and demolition waste is comprehensively introduced. Classified utilization of recycled materials from different kinds of waste and different target products are listed. DPF specific crusher is designed to overcome common problems raised in C&D waste production process, which is composed of rotors, external shell, drive system, and hydraulic system. Typical and novel screening and auxiliary equipment, particularly sand washing machines are compared. One-stage composite impact crushing pretreatment, roll crushing + roll grinding combined with recycling, and rolling + rolling combined with extrusion treatment process are the three major crushing technologies discussed in this chapter. Manufacturing system of sand and gravel aggregate of various disposing subjects (granite, hard materials, etc.) and requirements (350–400 t/h, 500 t/d, etc.) are demonstrated. Selected heavy metals can be utilized from industrial C&D waste both by winnowing enrichment and sequential stepwise leaching and electrolysis, in which process about 83–87.5% Pb and 88–92% Zn can be recovered. The recycling technologies and engineering application are further demonstrated in the four real projects (Shangrao city, Nantong city, Suzhou city, and Xi'an city). The overall process distribution, technical route, equipment, material balance, structures, target products, dust removal, water treatment, and labor organization are introduced as case studies. Wastes from both chemical and metallurgical industries have great reuse risk during recycling processes, with the risk index up to 113.8 and 44.6, respectively.

Keywords

Case study; Crushing; Engineering project; Metal recovery; Recycling technologies; Renewable wall materials; Risk assessment of recycled materials; Sand and gravel manufacturing

8.1. Leaching Characteristics of Recycled Concrete Generated From Heavy Metals–Contaminated Waste

Based on the results of pollution characterization, the most severely contaminated construction and demolition (C&D) waste was used as raw materials to produce recycled concrete blocks so as to reveal the leaching toxicity of recycled aggregates. Concentration of heavy metals of the six C&D wastes selected is listed in Table 8.1. The maximum content was: Cu (59,434.02 mg/kg), Zn (49,280 mg/kg), Pb (1054.34 mg/kg), Cr (7511.03 mg/kg), Cd (15.40 mg/kg), and Ni (2867.77 mg/kg), respectively.
The mix design of recycled concrete was based on the procedures for the Production of ordinary concrete. Natural aggregate (or gravel) was replaced by contaminated C&D waste.
Leaching experiments were performed using the HJ/T299-2007 method, and the results are listed in Table 8.2. The most severely contaminated C&D waste by Cu was obtained in the copper workshop from an electroplating factory, with an amount of 59,434.02 mg/kg and the leaching amount of 4.19 mg/L, higher than the Integrated wastewater discharge standard (2.0 mg/L) but lower than the Standard for pollution control on the security landfill site for hazardous wastes (75 mg/L). Results indicated that these kinds of C&D waste should not be disposed randomly but could be sent to landfill site as hazardous wastes. The leaching amount lowered to 0.75 mg/L after it was produced into recycled aggregates, lower than the Standards for drinking water quality and Environmental quality standards for surface water (level III).
The most severely contaminated C&D waste by Zn was obtained in the zinc electrolysis workshop, with an amount of 49,280 mg/kg and the leaching amount of 4.29 mg/L. The highest leaching amount of the six wastes was 5.17 mg/L, higher than the Integrated wastewater discharge standard (5 mg/L). The two highest leaching amounts of C&D waste after being produced into recycled products were 1.19 and 1.09 mg/L, both higher than the Environmental quality standards for surface water (level III), which indicated that they had potential risk to the surface water. No Zn was detected in the leachate of aggregates produced by other Zn-contaminated C&D wastes.

Table 8.1

Maximum Content of Heavy Metals in Contaminated Construction and Demolition (C&D) Waste

C&D WasteHeavy Metal (mg/kg)
CuZnPbCrCdNiAs
Cu-CI859,434.02a3685.827.5697.362.24591.11132.50
Zn-MI13743.7449,280412.45113.3313.65101.12155.09
Pb-MI2982.72467.591054.34461.87NDb68.6918.37
Cr-CI9309.66290.55438.907511.03ND10.2118.84
Cd-MI2476.3629,738.72879.4583.2915.4034.09232.31
Ni-CI103190.11312.8358.84306.46ND2867.7717.20
Max59,434.0249,2801054.347511.0315.402867.77232.31
Min82.72467.597.5683.29ND10.2117.20
De/Anc6/66/66/66/63/66/66/6
TVHM (level-I)3510035900.24015
TVHM (level-II)1002503002000.66025
TVHM (level-III)400500500300120040

image

CI, chemical industry; MI, metallurgical industry; TVHM, “the threshold values of heavy metals level III (CEPA, GB 15618-1995).”

a Average ± SD.

b Undetected.

c Samples in which pollutants were detected/all samples.

The most severely contaminated C&D waste by Pb was the firebrick in steelmaking plant, the amount was 1054.34 mg/kg and the leaching amount was 0.04 mg/L, higher than the Standards for drinking water quality (0.01 mg/L), but lower than the Environmental quality standards for surface water (level III) (0.05 mg/L). The highest initial leaching amount was 2.13 mg/L from the cleaning workshop in zinc factory, higher than the Integrated wastewater discharge standard (1.0 mg/L) but lower than the Standard for pollution control on the security landfill site for hazardous wastes (5 mg/L). It would cause aquatic pollution if abandoned, but landfill disposal was feasible. The leaching amount after recycling process was lower than the detection limit, which meant that the recycling process would largely reduce the environmental risk.

Table 8.2

Leaching Amounts of Heavy Metals From the Contaminated Construction and Demolition Waste Before and After Recycling

Heavy Metal (mg/L)
CuZnPbCrCdNiAs
Cu-CI8 BR4.195.17NDaNDND1.80ND
Cu-CI8 AR0.75 (82%)bND (100%)ND0.14 (−)NDND (100%)ND
Zn-MI1 BR1.194.290.50NDNDND0.93
Zn-MI1 AR0.49 (60%)1.19(72%)ND (100%)0.10 (−)NDND2.71 (−191%)
Pb-MI32 BR0.050.640.04NDNDNDND
Pb-MI32 ARND (100%)ND (100%)ND (100%)0.89 (−)NDNDND
Cr-CI9 BRNDNDND450.10NDNDND
Cr-CI9 ARNDNDND154.31 (66%)NDNDND
Cd-MI2 BR0.294.822.13NDNDND3.09
Cd-MI2 AR0.15 (48%)1.09 (77%)ND (100%)2.29 (−)NDND6.00 (−94%)
Ni-MI10 BR0.50NDND5.32NDNDND
Ni-MI10 AR0.10 (80%)NDND1.75 (67%)NDNDND
De/Anc9/126/123/128/120/121/124/12
dStandards for drinking water quality1.01.00.010.050.0050.020.05
eEnvironmental quality standards for surface water (level III)1.01.00.050.050.005-0.05
fIntegrated wastewater discharge standard2.05.01.01.50.11.00.5
gStandard for pollution control on the security landfill site for hazardous wastes75755120.5152.5
hIdentification standards for hazardous wastes100100515155

image

AR, after recycling; BR, before recycling; CI, chemical industry; MI, metallurgical industry.

a Undetected.

b Stabilization efficiency (percentage of the reduced leaching ratio).

c Samples in which pollutants were detected/all samples.

d Standards for drinking water quality (GB 5749-2006).

e Environmental quality standards for surface water (level III) (GB 3838-2002).

f Integrated wastewater discharge standard (China GB 8978-1996).

g Standard for pollution control on the security landfill site for hazardous wastes (China GB 18598-2001).

h Identification standards for hazardous wastes (China GB 5085.3-2007).

The most severely Cr-contaminated C&D waste was obtained in the Cr workshop from an electroplating factory, the amount was 7511.03 mg/kg and the initial leaching amount was 450.10 mg/L, which was 30 and 38 times that in the Identification standards for hazardous wastes and Standard for pollution control on the security landfill site for hazardous wastes, respectively, with huge environmental risk. Appropriate treatment should be performed before landfilling. Cr was detected in all the six leachate samples of recycled concrete. The highest amount was from the recycled concrete produced by C&D waste in Cr workshop from the electroplating factory, which was 154.31 mg/L, 10 times that in the Identification standards for hazardous wastes. The C&D waste should be treated properly before recycling.
The leaching amount of recycled aggregate produced by C&D waste from Ni workshop was 1.75 mg/L, which was higher than the Integrated wastewater discharge standard and lower than the Standard for pollution control on the security landfill site for hazardous wastes. It is worth pointing out that the leaching amount of four C&D wastes was lower than detection limit, whereas that of aggregate produced by these wastes was higher. The leaching amount of recycled aggregate produced by C&D waste from the cleaning workshop of Zn factory was 2.23 mg/L, which would cause aquatic pollution in its recycling process.
Most Cd in C&D waste was hard to be leached out. The results showed that none of the leachate of these samples contained Cd below detection limit, which indicated Cd had a relatively lower environmental risk.
The two most severely As-contaminated C&D waste was obtained in the cleaning workshop from zinc manufacturing factory and electrolysis plant, the amounts were 232.31 and 155.09 mg/kg, whereas the initial leaching amounts were 3.09 and 0.93 mg/L, respectively. However, the leaching amount of recycled aggregate was even higher, which was 6.0 and 2.71 mg/L, respectively. The former was higher than the Identification standards for hazardous wastes (5 mg/L), whereas the latter was higher than the Standard for pollution control on the security landfill site for hazardous wastes. Results indicated that As might cause a large environmental risk in the recycling of C&D waste.

8.1.1. Preparation of Metal-Contaminated Construction Materials

Six different construction materials were selected and the background content of heavy metals is listed in Table 8.3. The pollution concentration was set as 5000 mg/kg.

Table 8.3

Background Content of Heavy Metals in Six Different Construction Materials

SampleHeavy Metal (mg/kg)
CuZnPbCrCdNiAs
Cement brick–RS124.981057.4526.03245.16NDa27.9868.68
Foam concrete–RS528.22846.0934.0339.91ND10.5854.94
Brick–RS340.24328.1820.1974.20ND5.292.08
Dujiangyan recycled aggregate–RC328.671292.1525.6982.64ND21.0776.93
Pudong regeneration gravel–RC421.74115.5017.9552.96NDNDND
Steel firebrick–MI3211.4735.720.85269.64ND51.420.27
Max40.241292.1534.03269.64ND51.476.93
Min11.4735.720.8539.91NDNDND
De/Anb6/66/66/66/60/65/65/6
TVHM (level-I)3510035900.24015
TVHM (level-II)1002503002000.66025
TVHM (level-III)400500500300120040

image

MI, metallurgical industry; RC, recycled aggregates; RS, residential aggregates; TVHM, “the threshold values of heavy metals level III (CEPA,GB 15618-1995).”

a Undetected.

b Samples in which pollutants were detected/all samples.

8.1.2. Preparation of Recycled Concrete and Its Leaching Toxicity

Recycled concrete was produced by six different contaminated construction materials. Coir fiber was added to stabilize the heavy metals in the concrete. The coir fiber was treated with 2% NaOH so that various pores were generated on its service, which largely increased the combination between coir fiber and concrete. It could also increase the bending and compressive strength of the concrete products.
Three kinds of products were produced: normal recycled concrete, normal recycled concrete blocks with coir fiber, and alkali-treated recycled concrete blocks with coir fiber. Environmental risk of construction materials produced by contaminated C&D waste and the heavy metal stabilization effects of coir fiber were performed on the basis of the leaching toxicity. Results are shown in Table 8.4.
The leaching toxicity of the recycled concrete produced by six different construction materials is listed in Table 8.4. In general, the leaching amount of recycled concrete produced by steel fire bricks was the highest, followed by that produced by cement bricks. Those recycled concrete produced by foam concrete, red bricks, and recycled gravel had the lowest leaching capacity. Among all the heavy metals, Cd showed the highest leaching potentials, whereas Cu, Ni, and As showed the lowest. The leaching toxicity of recycled materials after treatment by coir fiber or alkali was lower than others.

Table 8.4

Leaching Toxicity of Recycled Concrete Produced by Six Different Construction Materials

SampleHeavy Metal (mg/L)
CuZnPbCrCdNiAs
A1-cement block-------
A2-standard recycled concrete0.009--0.346---
A3-coir fiber recycled concrete0.019--0.467---
A4-alkali-treated coir recycled concrete---0.21---
B1-foam concrete-------
B2-recycled concrete standards---0.178---
B3-coir fiber recycled concrete---0.128---
B4-alkali-treated coir recycled concrete---0.069---
C1-brick---0.344---
C2-standard recycled concrete---0.013---
C3-coir fiber recycled concrete---0.005---
C4-alkali-treated coir recycled concrete---0.0160.019--
D1-Dujiangyan recycled aggregate-------
D2-standard recycled concrete---0.121---
D3-recycled concrete coir fiber---0.078---
D4-alkali treated coir recycled concrete---0.107---
E1-Pudong recycled gravel-------
E2-standard recycled concrete---0.147---
E3-coir fiber recycled concrete---0.138---
E4-alkali-treated coir fiber recycled concrete---0.112---
F1-Baosteel firebrick-0.389-----
Table Continued

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SampleHeavy Metal (mg/L)
CuZnPbCrCdNiAs
F2-standard recycled concrete0.01831.0170.524-58.925--
F3-coir fiber recycled concrete----32.672--
F4-alkali-treated coir fiber recycled concrete0.05541.8230.632-68.642--
Standards for drinking water quality1.01.00.010.050.0050.020.05
Environmental quality standards for surface water (level III)1.01.00.050.050.005-0.05
Integrated wastewater discharge standard2.05.01.01.50.11.00.5
Standard for pollution control on the security landfill site for hazardous wastes75755120.5152.5
Identification standards for hazardous wastes100100515155

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