พฤติกรรมการดูดซับและการชะล้างโลหะหนักของดินเหนียวเบนโทไนท์ที่ผสมกับซีเมนต์และวัสดุปอซโซลาน จากการทดสอบแบบต่อเนื่อง

Abstract

The rapid growth of industries has led to the increasing of environmental problem. Every year, large amount of wastewater has been discharged into rivers without treatment. The wastewater is often contaminated with high amounts of heavy metals. Adsorption is one of the methods for heavy metal removal. Clay have been widely used as the adsorbent for wastewater treatment. This research focuses on the adsorption of zinc and nickel on bentonite clay when mixing with various Cement and Pozzolanic materials by column leaching test. The Pozzolanic materials in this study were 1) fly ash, 2) bottom ash, 3) silica fume, 4) blast furnace slag, 5) metakaolin, and 6) rice husk ash. The column leaching test was divided into 3 cycles. The heavy metals solution were released in the first cycle to the example model with continuous flow to simulate the actual condition of wastewater discharging into the soil. Distilled water was released in the second cycle with continuous flow to simulate the desorption process by rain. The last cycle was then carried out to verify the adsorption capability after the desorption process. The adsorption behavior in this study can be illustrated in breakthrough curves. The breakthrough curves present a relationship between the rates of absorption versus service time. The retardation factor (R) and Diffusion coefficient (D) can be calculated from breakthrough curves. In this study, bentonite mixed with cement showed the highest adsorption performance for both zinc and nickel. Bentonite mixed with cement had more retardation factor than bentonite to 1.41 times, and had less diffusion coefficient than bentonite to 4 times. The adsorption of bentonite decreased when bentonite was mixed with Pozzolanic materials. The efficiency of pozzolanic materials can be ranked as follows: cement > fly ash > bottom ash > blast furnace slag > metakaolin > silica fume > rice husk ash. Comparing the results, it was shown that zinc was adsorbed by bentonite mixed Cement and Pozzolanic materials better than nickel.  The desorption process in second cycle could not fully remove the heavy metals ions from the surface of the adsorption.