Symbols Used
CHAPTER 6 COMBINED EFFECT OF INORGANIC S ALTS AND HEAVY METALS ON
6.1. INTRODUCTION
6.2.3. Swelling pressure and Swelling potential
Swelling pressure is an important parameter for the design of structures like liners, as its swelling behaviour gets affected in presence of leachates. In order to prevent opening of cracks and fissures, liners must possess a high value of swelling pressure in order to suffice as impermeable barriers.
Table 6.4 and 6.5 shows the effect of the mixed salt solutions on the swelling potential and swelling pressure of both the bentonites. The data in Table 6.4 shows that the swelling pressure and swelling potential of both the bentonites decreased significantly due to interaction with the mixed salt solution. The effect of mixed salt solution on Bentonite-B
was more significant in comparison to Bentonite-A. The swelling pressure of Bentonite-B was decreased from 697.2 kPa to 271.7 kPa due to increase in the concentration from 0 (i.e.
DI water) to 1 N CaCl2+0.1 N NaCl solution.
Similar to the observation made in the liquid limit, a comparison between the data in Table 6.4 and Fig. 4.11 shows that the combined effect of salts has a significant impact on the swelling pressure of both the bentonites in comparison to the individual salt solution indicating an additive effect of salt on swelling pressure. The data in the Table 6.4 shows that the swelling pressure of the Bentonite-B in the presence of 0.1 N CaCl2+0.1 N NaCl was determined to be 350.1 kPa, whereas, it was found to be 418.7 kPa for 0.1 N of NaCl and 392.1 kPa for 0.1 N of CaCl2 solution (from Fig. 4.11). Similarly, the swelling pressure of the Bentonite-A in the presence of 0.1 N CaCl2+0.1 N NaCl was found to be 190.2 kPa, whereas, it was found to be 186.3 kPa for 0.1 N of NaCl and 176.5 kPa for 0.1 N of CaCl2 solution.
The data for the swelling pressure for both the bentonites in presence of heavy metals shows that the combined effect of the heavy metals was quite significant in comparison to the individual effect. The data in Table 6.4 shows that the swelling pressure of Bentonite-B was 409.8 kPa with a mixture of 1000 ppm of solution of Cu2+, Zn2+ and Pb2+ as the pore fluid, whereas, for the individual solution of 1000 ppm of Cu2+, Zn2+ and Pb2+ it was 441.2, 519.9 and 580.1 kPa, respectively indicating an additive effect of heavy metals on the swelling pressure of the bentonites as well.
However when 1000 ppm of the Cu2+, Zn2+ and Pb2+ was added with 1 N CaCl2 + 0.1 N NaCl and 1 N NaCl+0.1 N CaCl2, the swelling pressure of the bentonites decreased considerably. From the data in the Table 6.4 it can be seen that the swelling pressure of Bentonite-B decreased from 271.7 kPa to 221.6 kPa due to the addition of 1000 ppm of Cu2+, Zn2+ and Pb2+ solution to 1 N CaCl2 + 0.1 N NaCl solution. This observation was
contrary to the observation made for the liquid limit where a marginal decrease due to addition of 1000 ppm of Cu2+, Zn2+ and Pb2+ was observed.
Table 6.4 Swelling pressure of Bentonite-A and -B in presence of the solutions Combinations of salt solutions Swelling pressure (kPa)
Bentonite-A Bentonite-B
DI water 267.7 697.2
0.1 N CaCl2 + 0.1 N NaCl 190.2 350.1
1 N CaCl2 + 0.1 N NaCl 180.3 271.7
1 N NaCl + 0.1 N CaCl2 210.0 315.0
100 ppm of all HM 227.1 583.4
1000 ppm of all HM 205.9 409.8
1 N CaCl2 + 0.1 N NaCl + 100 ppm of all HM 176.2 268.6 1 N CaCl2 + 0.1 N NaCl + 1000 ppm of all HM 168.6 221.6 1 N NaCl + 0.1 N CaCl2 + 100 ppm of all HM 202.9 312.8 1 N NaCl + 0.1 N CaCl2 + 1000 ppm of all HM 200.1 250.1 0.1 N NaCl + 0.1 N CaCl2 + 100 ppm of all HM 184.0 348.1 0.1 N NaCl + 0.1 N CaCl2 +1000 ppm of all HM 174.5 293.2
However, the data in Table 6.5 on the effect of mixed salt solution on the swelling potential indicates that the mixed salt solution decreased the swelling potential marginally in comparison to the individual salt solution. Bentonite-B exhibited a swelling potential of 28.9 % due to the permeation of 0.1 N CaCl2+0.1 N NaCl in comparison to 29.0 % for 0.1 N of NaCl and 31.1 % for 0.1 N CaCl2 solutions (Fig. 4.8). Similarly, the swelling potential of Bentonite-B in the presence of 1 N CaCl2+0.1 N NaCl was observed to be 18.3
%, whereas, for 1 N of CaCl2 it was 21.4 % (Fig. 4.8).
Table 6.5 Swelling potential of Bentonite-A and -B in presence of the solutions Combinations of salt solutions Swelling potential (%)
Bentonite-A Bentonite-B
DI water 22.1 48.4
0.1 N CaCl2 + 0.1 N NaCl 21.4 28.9
1 N CaCl2 + 0.1 N NaCl 15.3 18.3
1 N NaCl + 0.1 N CaCl2 16.3 19
100 ppm of all HM 21.9 43.4
1000 ppm of all HM 20.9 33.9
1 N CaCl2 + 0.1 N NaCl + 100 ppm of all HM 14.7 17.3 1 N CaCl2 + 0.1 N NaCl + 1000 ppm of all HM 14.1 16.6 1 N NaCl + 0.1 N CaCl2 + 100 ppm of all HM 15.8 16.8 1 N NaCl + 0.1 N CaCl2 + 1000 ppm of all HM 15.4 16.1 0.1 N NaCl + 0.1 N CaCl2 + 100 ppm of all HM 20.9 27.0 0.1 N NaCl + 0.1 N CaCl2 + 1000 ppm of all HM 19.5 24.6
The data for the heavy metals in Table 6.5 shows that the swelling potential for the mixture of 100 ppm of Cu2+, Zn2+ and Pb2+ solution was observed to be 43.4 % for Bentonite-B.
For the individual concentration of 100 ppm of Cu2+, Zn2+ and Pb2+ solution swelling potential value of 42.4 %, 42.8 % and 45.4 % was observed respectively (Fig. 5.5).
Similarly, the swelling potential with the mixture of 100 ppm of Cu2+, Zn2+ and Pb2+
solution was observed to be 21.9 % for Bentonite-A. For the individual concentration of 100 ppm of Cu2+, Zn2+ and Pb2+ solution 20.9 %, 20.8 % and 21.2 % of swelling potential value was observed respectively. Similar to the effect on the swelling pressure, the addition of the mixtures of 1000 ppm of Cu2+, Zn2+ and Pb2+ solution to the 1 N NaCl+0.1 N CaCl2
and0.1 N NaCl+1 N CaCl2 produced a significant decrease in the swelling potential. With the addition of mixture of 1000 ppm of Cu2+, Zn2+ and Pb2+ solution to the 1 N NaCl+0.1 N CaCl2 decreased the swelling potential of Bentonite-B from 19 % to 16.1 %. With the
addition of 1000 ppm of Cu2+, Zn2+ and Pb2+ solution to the 0.1 N NaCl+0.1 N CaCl2
decreased the swelling potential of Bentonite-B from 28.9% to 24.6%.