Indian Geotechnical Conference (December 18-20, 2003) s11

IGC 2009, Guntur, INDIA An Accelerated Column Test for Studying Sorption Property of Soil

AN ACCELERATED COLUMN TEST FOR STUDYING SORPTION PROPERTY OF SOIL

B. Poly Research Scholar, Department of Civil Engineering, IIT Guwahati, Guwahati–781 039, India. E-mail: [email protected]. K.D. Chanchal Postgraduate Student, Department of Civil Engineering, IIT Guwahati, Guwahati–781 039, India. E-mail: [email protected] S. Sreedeep Assistant Professor, Department of Civil Engineering, IIT Guwahati, Guwahati–781 039, India. E-mail: [email protected]

ABSTRACT: One of the major challenges faced by the developing countries like India is the efficient management of incredible quantity of wastes that are generated. Engineered landfill is an efficient method for meeting this challenge. The most significant chemical property of the soil used in landfill liners is the contaminant retention capacity or sorption. Different methodologies like batch test and column test have been used for measuring the sorption properties of soil. But it can be noted that the real life scenario can be better stimulated by the use of column test. However, for a well compacted soil this method has the limitation of being more time consuming. So, a new approach is needed that makes the procedure less time intensive. To achieve this, a new accelerated column test set up based on vacuum application for determining sorption property of the soil has been fabricated. The methodology has been demonstrated by determining the sorption property of a locally available soil with potassium as the model contaminant.

1. INTRODUCTION been demonstrated by determining sorption of a locally available soil with potassium as the model contaminant. Rapid urbanization, industrialization and population growth has resulted in an indiscriminate production in huge volume of wastes which are disposed off into surface dump yards, or 2. THEORETICAL BACKGROUND engineered/non-engineered landfill sites. In the due course of The determination of sorption characteristics from column time, ecological harmony gets disturbed as the waste interacts test is based on the well established Advection-Dispersion with water and produces leachates and gases which pollute Equation (ADE) (Shukla et al. 2002) as represented by Eqn. 1, the geo-hydrosphere (Selim & Iskandar 1999). Such a situation 抖C2 Cv C has necessitated efficient waste containment facilities to Rt= D t - t (1) 秖th 2 x effectively contain the contaminants. The contaminant retention x property of soil used in these waste containment facility is of where R is the retardation factor representing sorption behavior, utmost importance for effective containment of waste and  is the volumetric water content, Ct is the concentration minimizing groundwater pollution. corresponding to time t, Dh is the hydrodynamic dispersion coefficient (=  . vs + De),  is the dispersion coefficient, vs is The retention property of soil is defined based on the sorption the seepage velocity, De is the effective diffusion coefficient, characteristics of a particular soil-contaminant system. 24 hrs x is the distance, v is discharge velocity. A higher value of R batch test and column test are utilized by researchers for indicates higher sorption. The solution of Eqn. 1 corresponding characterizing sorption. Even though, batch test are simple, it to different boundary conditions (Freeze & Cherry 1979; has the disadvantage of overestimating the retention capacities Toride et al. 1999) give theoretical Break Through Curve of soil due to relatively high liquid to solid ratio (Koivalla (BTC), which is a graphical plot between relative concentration et al. 2008). Column test, on the contrary, depicts a more of solute (Ct/C0) and cumulative pore volume/time, where C0 realistic situation existing in the field. However, the test is the initial concentration of contaminant. In the present would be quite time-consuming if the soil is well compacted. study, R value is obtained by fitting theoretical BTC determined To overcome this issue, the present study attempts to develop for the appropriate boundary condition using contaminant an accelerated column set up based on vacuum application transport software Cxtfit (Toride et al. 1999) to the experi- for studying the sorption property of soil. The test set up has mental BTC from column test.

40 An Accelerated Column Test for Studying Sorption Property of Soil 3. MATERIALS AND METHODS Throughout the test period the height of KCl solution was maintained constant. A locally available red soil (designated as RS) used in this study is subjected to various physico-chemical tests such as specific gravity, particle size distribution, Atterberg limits Column etc. by following the guidelines provided in the literature (ASTM D 4.08). The total SSA was determined using ethylene KCl solution glycol monoethyl ether and CEC was determined by Moisture Vacuum Trap Pump ammonium replacement method (Horneck et al. 1989). The Soil summary of these characterizations is listed in Table 1.

Table 1: Summary of Physico-Chemical Properties of Soil Effluent collection Figure not to scale Tests Value s Specific gravity 2.62 Fig. 1: Experimental Column Setup Particle size (%) Clay 22 4. RESULTS AND DISCUSSION Silt 46 Sand 32 For obtaining theoretical BTC, single step input of the contaminant with initial normalized concentration (Ct/C0) Liquid limit (%) 46 equal to one was considered. Darcy velocity of flow and Plastic limit (%) 27 dispersion coefficient is taken as 10–5 m/s and 10–6 m2/s. Plasticity index (%) 20 Based on these values, theoretical BTC has been fitted to the Classification (USCS) CL experimental data, as depicted in Figure 2. This would give the best fit value of retardation factor based on non-linear Maximum dry density (g/cc) 1.87 regression. It can be noted from the figure that the analytical Optimum moisture content (%) 15 solution fits reasonably well to the measured column test CEC (meq./100g) 16.07 result with a coefficient of determination equal to 0.8999. Total SSA (m2/g) 94.12 The best fit theoretical BTC to the experimental data resulted in the retardation factor (R) of 9.27. A higher value of retardation factor may be attributed to the higher surface area The column set up used in the present study, as depicted in of the soil used in the study. Figure 1, essentially consists of a perspex cylinder having a diameter of 2.5 cm and 10 cm height, connected to a vacuum pump via effluent collection conical flask and moisture trap. 1.0 Measured Fitted Adequate quantity of soil was mixed with required amount of water and kept for maturation for two days. The soil was then 0.8 compacted to a height of 3 cm corresponding to optimum 0 0.6 C / t

moisture content and maximum dry density. Two filter papers C 0.4 were placed at the top and bottom of the soil column. In addition, a perspex plate is placed at the bottom for uniform 0.2 collection of solution flowing through the soil column. When 0.0 vacuum pressure is applied, solution flowing through the soil 0 10k 20k 30k 40k 50k mass gets collected in the effluent collection conical flask. Time (s) Moisture trap has been provided to prevent the moisture entering the vacuum pump. Due to vacuum application, the Fig. 2: Measured and Predicted Breakthrough Curve time required for flow will be less as compared to free for 106 mg/l of K+ gravity flow. Prior to the start of the test, the soil column was water saturated. 5. CONCLUSIONS Further, water was replaced by 106 mg/l of KCl and allowed This paper presents the details of an accelerated column test to flow through the soil column under a constant hydraulic set up based on vacuum application for quick determination gradient of 1.2. The effluent collected at different interval of of sorption property of the soil. The usefulness of the test set time has been analyzed for potassium ion (K+) concentration up has been demonstrated by evaluating sorption of potassium (Ct) using an ion chromatograph (Metrohm, Switzerland). ion on locally available soil compacted at optimum compaction

41 An Accelerated Column Test for Studying Sorption Property of Soil condition. It is noted from the study that the best fit theoretical Koivula, P.M., Kujala, K., Ronkkomaki, H. and Makela, M. breakthrough curve to the experimental data resulted in the (2008). “Sorption of Pb(II), CR(III), Cu(II), AS(III) to retardation factor (R) of 9.27. Peat, and Utilization of the Sorption Properties in Industrial Waste Landfill Hydraulic Barrier Layers”, J.l of REFERENCES Hazardous Materials 164: 345–352. Selim and Iskandar (1999). “Fate and Transport of Heavy ASTM 4.08-06 (2006). ASTM Book of Standards Volume 4.08: Metals in the Vadose Zone”, Lewis, London. Construction: Soil and Rock (I), Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA, Shukla, M.K., Kastanek, F.J. and Nielsen, D.R. (2002). USA. “Inspectional Analysis of Convective-Dispersion Equation and Applications on Measured Breakthrough Curves”, Freeze, R.A. and Cherry, J.A. (1979). Groundwater, Prentice Hall, Inc. Soil Science Society of America J.l, 66(4):1087–1094. Horneck, D.A., Hart, J.M., Topper, K. and Koespell, B. Toride, N., Leil, F.J. and van Genuchten, M. Th. (1999). (1989). “Methods of Soil Analysis Used in the Soil “The CXTFIT Code for Estimating Transport Parameters Testing Laboratory” at Oregon State University. Agric. from Laboratory or Field Tracer Experiments Version Exp. Stn. S.M. 89: 4. 2.1”, Research Report, U.S. Salinity Laboratory, No. 137, California.