Adsorption of nickel and zinc by residual soils

Abstract

Soil has long been utilized as low cost liner material to prevent contamination from leachate to groundwater media. To find a suitable soil material for this purpose is a great challenge. This study describes the potential use of residual soil to functions as engineered clay liner for waste disposal landfill in Malaysia. Three types of residual soils were investigated namely marine clays (SBMC1, SBMC2), Residual Granites (BGR, KGR) and residual meta-sediments (BBMS1, BBMS2 and PMS). Physical and chemical tests were applied for both granitic soils to determine the physical and chemical properties of soil materials. Physical and chemical tests involved grain size distribution, Atterberg limits, compaction, pH, organic content, specific gravity, Cation Exchange Capacity (CEC) and Specific Surface Area (SSA) as well as Batch Equilibrium Test for adsorption of heavy metals. The best potential soil materials for clay liner is the materials that have high pH value, high organic matter, high liquid and plastics limits, high CEC and SSA values. The best material also highly dominated with clay (in this case PKMC, SBMC1 and SBMC 2). Result show the range of pH values are from 6.95-8.36, range of organic content are from 4.35-6.41%, the specific conductivity values range from 2.13-2.34 and for liquid limit and plastic limit range are from 56.40-84 and 26.86-59.35% respectively; which is high to very high plasticity. Residual soils as low-cost adsorbent materials were also used for removal of Nickel (Ni) and Zinc (Zn) from aqueous solutions. Batch test was used and the effect of heavy metal concentration was studied. Results were analyzed using adsorption isotherm models (i.e., Linear, Langmuir and Freundlich). Based on the correlation coefficient (r2 values), most of residual soils fitted nicely to Linear, Langmuir and Freundlich models. For Ni, most soils fitted to Langmuir models except for meta-sediment while for Zn fitted to Linear model. Marine clay has the highest adsorption coefficient ranged between KL = 0.2380-0.9655 L kg −1 followed by granite and meta-sediment KL = 0.0031-0.0168 L kg −1 and KL = 0.0016-0.0075 L kg −1 respectively. While for Zn, marine clay also has the best adsorption coefficient ranged between Kd = 0.0453-0.1249 L kg −1, followed by granite and meta-sediment ranged between Kd = 0.0027-0.0028 L kg −1 and Kd = 0.0012-0.0016 L kg −1. The selectivity sequence KL for Ni is SBMC2> SBMC1 > PKMC> BGR> PMS> KGR> BBMS2> BBMS1 while for Zn, the selectivity sequence of Kd is SBMC2> SBMC1> PKMC> BBMS1> BBMS2> PMS>BGR> KGR. The study concludes that marine clay is the best material for landfill clay liner due to suitable physical-chemical characteristics and also appeared to be the best natural adsorbent of Ni and Zn of metal concentration in solution.