Effect of co-existing ions on lead leaching behaviour from hardened - - PowerPoint PPT Presentation
4th International Conference on Rehabilitation and Maintenance in Civil Engineering Best Western Premier Hotel, Solo Baru, July,11 12 2018 Effect of co-existing ions on lead leaching behaviour from hardened cement paste Takumi Nishiwaki
Takumi Nishiwaki Shaojun Zhou Masaharu Yamasaki Yuko Ogawa Kenji Kawai
4th International Conference on Rehabilitation and Maintenance in Civil Engineering Best Western Premier Hotel, Solo Baru, July,11‐12 2018
Industrial wastes
concrete expectation
Recently, due to environmental problems, a recycling-oriented society is required. In the concrete field, concrete made from industrial wastes is expected. Environmental issues happen Industrial wastes
expectation concrete
However, some industrial wastes contain harmful heavy metals .
Risk of leaching heavy metals
Therefore utilizing the industrial wastes may be dangerous, due to the leaching of heavy metals which are harmful for human bodies and environment.
Heavy metals
In Cement paste, Portlandite, Ettringite and CSH have an ability to adsorb and fix heavy metals. Previous study 1 In CaCl2 solutions, the leaching amount is larger than the amount in deionized water. The leaching amount in CaCl2 solutions is 35-40 times as much as the amount in deionized water. Previous study 2
deionized water CaCl2・2H₂O
It is necessary to investigate the leaching behaviour of lead in different circumstances.
In this study The leaching behaviours of lead from cement pastes immersed in three kinds of chloride solutions as well as those in deionized water were examined.
Focusing on the difference of Ca(OH)2 content, the relationship between leaching amount and Ca(OH)2 content was investigated.
Specimens (Cement paste) W/C : 0.40, 0.55 Water : Pure water Lead : 1 mass% of cement.
atomic absorption spectrophotometer
40mm 40mm 40mm
Pb
Tank Leaching Test On 0.25,1,2.25,4,9,16,25,36,64 days from the beginning, all solutions were changed. The concentrations of lead leaching was determined by an atomic absorption spectrophotometer.
solution concentration NaCl 5,10,20% KCl 5,10,20% CaCl2 5,10,20% deionized water ー
Solution’s types of tank leaching test
mixture W/C Unit content [kg/m³] Addition[㎏/m³] Water Cement lead Pb40 0.40 558 1394 13.94 Pb55 0.55 634 1153 11.53
Tank Leaching Test On 0.25,1,2.25,4,9,16,25,36,64 days from start, all solutions were changed. The concentrations of lead leaching was determined with an atomic absorption spectrophotometer.
solution concentration NaCl 5,10,20% KCl 5,10,20% CaCl2 5,10,20% deionized water ー
TG-DTA After 64days of immersion, TG-DTA test was carried out to measure Ca(OH)2 content. The relation between the amount of lead leaching and Ca(OH)2 content. 0-0.1mm from surface
20 40 60 80 100 120 140 5 10 Cumulative leaching amount of lead(mg/kg) Duration（√day） CaCl2 10% KCl 10% NaCl 10% H2O
Focusing on 10% solutions (W/C=0.40),
(the amount of lead leaching[mg/kg]) =（the amount of lead leaching[mg])/(the mass of specimens[kg])
➢ The largest amount of lead was leached in CaCl2 solutions, followed by KCl solutions, NaCl solutions and deionized water. ➢ The lead leaching amount in 10%-CaCl2 solution was approximately 35 times as much as that in deionized water. 35times
Focusing on all solutions (W/C=0.40)
50 100 150 200 250 300 5 10 Cumulative leaching amount of lead(mg/kg) Duration(√day) CaCl2 20% CaCl2 10% CaCl2 5%
2 4 6 8 10 12 14 16 5 10 Cumulative leaching amount of lead(mg/kg) Duration(√day) KCl 10% KCl 5% KCl 20% 2 4 6 8 10 12 5 10 Cumulative leaching amount of lead(mg/kg) Duration(√day) NaCl5% NaCl10% NaCl20%
The lead leaching amount was almost proportional to the concentration of the solutions in the case of CaCl2 solutions. On the other hand, the lead leaching amount had no correlation with the concentration of solutions in the case of KCl solutions and NaCl solutions.
Focusing on all solutions (W/C=0.40)
50 100 150 200 250 300 5 10 Cumulative leaching amount of lead(mg/kg) Duration(√day) CaCl2 20% CaCl2 10% CaCl2 5%
2 4 6 8 10 12 14 16 5 10 Cumulative leaching amount of lead(mg/kg) Duration(√day) KCl 10% KCl 5% KCl 20% 2 4 6 8 10 12 5 10 Cumulative leaching amount of lead(mg/kg) Duration(√day) NaCl5% NaCl10% NaCl20%
The lead leaching amount was almost proportional to the concentration of the solutions in the case of CaCl2 solutions. On the other hand, the lead leaching amount had no correlation with the concentration of solutions in the case of KCl solutions and NaCl solutions.
50 100 150 200 250 300 5 10 Cumulative leaching amount of lead(mg/kg) Duration(√day) CaCl2 20% CaCl2 10% CaCl2 5% H2O 2 4 6 8 10 12 14 16 5 10 Cumulative leaching amount of lead(mg/kg) Duration(√day) KCl 10% KCl 5% KCl 20% NaCl5% NaCl10% NaCl20% H2O
𝜖𝐷 𝜖𝑢 = 𝐸 𝜖2𝐷 𝜖𝑦² → M=2C₀S
Dt 𝜌
The results imply that the leaching of lead is primarily caused by the diffusion of lead. Besides, the concentration gradient of lead ions is changed for some reasons around 4 to 9 days of immersion. Fick’s second law
C; Concentration of lead(mg/cm^3) C0; Initial content of lead(mg/cm^3) t; time(s) D; Diffusion coefficient (m²s⁻¹) M; Cumulative amount (mg) S; Surface area (m²)
Further investigation will be needed to clarify the reason.
1 2 3 4 5 6 7 8 9
CaCl2 5% CaCl2 10％ CaCl2 20％ Leaching rate(%) W/C=0.55 W/C=0.40
0.1 0.2 0.3 0.4 0.5 Leaching rate(%) W/C=0.55 W/C=0.40
Leaching rate
(Leaching rate[%])= (Cumulative leaching amount(mg)) ( Initial content mg )
x100
➢ The leaching rate in 20% CaCl2 solution was highest in all solutions. ➢ The rate of W/C=0.55 in CaCl2 solution (highest in all specimens) was only 8%.
→Thus, it was shown most parts of specimens were not affected by chloride solutions and deionized water.
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 Content of Ca(OH)2(%)
2 4 6 8 10 12 14 16 18 20 Content of Ca(OH)2(%)
Ca(OH)2 content
➢ The Ca(OH)2 content decreased since immersion.
→Thus, all specimens could reduce an ability to fix heavy metal ions.
(Previous study shows Ca(OH)2 has an ability to fix heavy metal ion.) ➢ The difference of the Ca(OH)2 content between the specimens with W/C=0.40 and W/C=0.55 is very small.
W/C=0.40 W/C=0.55
reduce reduce
1 2 3 4 5 6 7 8 9
CaCl2 5% CaCl2 10％ CaCl2 20％ Leaching rate(%) W/C=0.55 W/C=0.40
0.1 0.2 0.3 0.4 0.5 Leaching rate(%) W/C=0.55 W/C=0.40
Leaching rate
The leaching rate for the specimens with W/C=0.40 is lower than that with W/C=0.55 in each case. The difference of the lead leaching amount in W/C is related to factors other than the difference of the Ca(OH)2 content. The difference of pore structure may affect this phenomenon.
(Leaching rate[%])= (Cumulative leaching amount(mg)) (Initial content mg )
x100
50 100 150 200 250 300 5 10 Cumulative amount of lead leaching (mg/kg)(64day) Content of Ca(OH)2(%) CaCl₂5% CaCl₂10% CaCl₂20% KCl5% KCl10% KCl20% NaCl5% NaCl10% NaCl20% H₂O
There is no relationship between the cumulative leaching amounts of lead and the Ca(OH)2 content in the specimens after immersion.
Relationship between lead leaching amount (W/C=0.40) and Ca(OH)2 content
50 100 150 200 250 300 1 2 3 Cumulative amount of lead leaching (mg/kg)(64day) Content of Ca(OH)2(%) CaCl₂5% CaCl₂10% CaCl₂20% 2 4 6 8 10 12 14 16 2 4 6 8 Cumulative amount of lead leaching (mg/kg)(64day) Content of Ca(OH)2(%) KCl5% KCl10% KCl20% NaCl5% NaCl10% NaCl20% H₂O
➢ From the results of the tank leaching test, the largest leaching amount of lead was observed in CaCl2 solution, followed by KCl solution, NaCl solution and deionized water. ➢ In the case of CaCl2 solution, the lead leaching amount increased as the concentration of the solution increased. However, in the case of KCl solution and NaCl solution, the lead leaching amount was almost the same regardless of the concentration. ➢ Based on the results of the Ca(OH)2 content after immersion in the vicinity
leaching amount in the type of solution is not directly related to the Ca(OH)2 content in the specimen after immersion.
References 1.Kawai, K., Kikuchi, H., Takaya, H., and Hayashi, A. Adsorption and Desorption Properties and Leaching Behavior of Lead in Cement Hydrates, Cement Science and Concrete Technology, 65,
2.Uchikawa, H, Fixation of hazardous substance in waste and sludge by cement Ceramics, 12, pp.103-117 (1977)
Focusing on W/C=0.55,
(the amount of lead leaching[mg/kg]) =（the amount of lead leaching[mg])/(the mass of specimens[kg])
50 100 150 200 250 300 350 400 450 500 5 10 Cumulative leaching amount
Duration (√day) CaCl₂20% CaCl₂10% CaCl₂5% H₂O 5 10 15 20 25 30 5 10 Cumulative leaching amount
Duration (√day) KCl20% KCl5% NaCl5% KCl10% NaCl10% NaCl20% H₂O
Focusing on CaCl2 solutions,
50 100 150 200 250 300 5 10 Cumulative leaching amount of lead(mg/kg) Duration(√day) CaCl2 20% CaCl2 10% CaCl2 5% H2O
Previous study show Concrete is deteriorate in high concentration CaCl2 solution. One of the causes of this phenomenon is generation of 3CaO・CaCl2・15H2O. 3Ca(OH)2＋CaCl2＋12H2O → 3CaO・CaCl2・15H2O In this study, the cause which leaching amount was highest in CaCl2 solutions can be deterioration to generate 3CaO・CaCl2・15H2O in the specimens.
Deterioration of hardened cement pastes immersed in calcium chloride chloride solution, Hiroaki MORI, Ryuichiro KUGA, Shoichi OGAWA and Yoshimori KUBO , Cement Science and Concrete Technology, Vol.66, 2012
Focusing on W/C=0.40,
Portlandite Ettringite Friedel’s salt Damaraite
10 20 30 40 50 60 70 before H2O KCl NaCl CaCl₂ Percentage content of CSH(%)
CSH content
Decreasing Portlandite and Ettringite was confirmed. Increasing CSH was also confirmed. However, it was not clear the relation between their changing amount and immersed solution. Damaraite was confirmed in the specimens immersing chloride solutions. Quantitative analysis Qualitative analysis
0.1 1 10 100 9.5 10.5 11.5 12.5 13.5 Leaching amount(mg/kg) pH CaCl2 10% CaCl2 20% CaCl2 5% KCl 5% KCl10% KCl20% NaCl 5% NaCl 10% NaCl 20% H2O These figures show there were a relation between leaching amount and pH . However, it wasn’t clear that pH affected the leaching amount dominantly.
1 10 100 9.5 10.5 11.5 12.5 Leaching amount(mg/kg) pH CaCl2 20% CaCl2 10% CaCl2 5%
0.1 1 10 11.5 12 12.5 13 Leaching amount(mg/kg) pH KCl 5% KCl10% KCl20% NaCl 5% NaCl 10% NaCl 20% H2O
㏗
100 200 300 400 500 600 2 4 6 Cumulative amount of lead leaching (mg/kg)(64day) Content of Ca(OH)2(%) CaCl₂5% CaCl₂10% CaCl₂20% KCl5% KCl10% KCl20% NaCl5% NaCl10% NaCl20% H₂O
Relation between lead leaching rate (W/C=0.55) and amount of Ca(OH)2
There is no relationship between the cumulative leaching amounts of lead and the Ca(OH)2 content in the specimens after immersion.
100 200 300 400 500 600 1 2 3 4 Cumulative amount of lead leaching (mg/kg)(64day) Content of Ca(OH)2(%) CaCl₂5% CaCl₂10% CaCl₂20%
5 10 15 20 25 30
2 4 6
Cumulative amount of lead leaching (mg/kg)(64day) Content of Ca(OH)2(%) KCl5% KCl10% KCl20% NaCl5% NaCl10% NaCl20% H₂O