Determination Of MTBE In Black Soil And The Study Of The Sorption Characterization Of MTBE By Black Soil

Methyl tert-butyl ether is a kind of gasoline additive. It was put into use in the early 1980s, and now, it was still widely utilized in many country. Along with the in-depth study of MTBE, people found that its presence in environment causes a widespread pollution and poses a serious threat to human health. Most of study in the past focused on the pollution and remediation of MTBE to water body. But the researches of the pollution of MTBE to soil were less. This experiment took different kind of black soil for experimental soil, and set up a new method to detected MTBE in black soil with static headspace gas chromatography. And based on the method, the adsorption kinetics and thermodynamics behavior of MTBE absorbed by black soil in water solution were systemically researched. At the same time, the situation of the pollution of MTBE in soil around Changchun city was researched. At last, further research direction was put forward.1. The preliminary treatment condition of the soil samples was optimized. The samples were extracted with four kinds of extraction agent of different concentration, they were redistilled water, NaCl, Na₂SO₄ and K₂SO₄. The result showed that when extracted with redistilled water, the extraction rate is 88%, which was the highest among the results of the extraction agent. When the samples were extracted with NaCl, the extraction rate decreased dramatically along with the increase of NaCl concentration. When the samples were extracted with Na₂SO₄, the extraction rate decreased along with the increase of Na₂SO₄ concentration, too. And when extracted with K₂SO₄, there was nearly no effect to the extraction rate. When extracted with 5% NaCl, Na₂SO₄ and K₂SO₄, the extraction rate was 75.2%, 79.7% and 75.7% respectively. The extraction rate was only 14.2% when extracted with saturated NaCl solution. The effect of time and temperature on extraction rate showed that when the samples were extracted for 40min at room temperature, the result was satisfied.2. The leaching solution was centrifugalized, and then distilled by headspace analytical method. The main factor that influenced the sensitivity of the method was the headspace thermostat temperature and time and the salting-out. The result expressed: increasing the temperature could increase the sensitivity, but if the temperature was too high, the analytical accuracy would decrease. The research showed that when the temperature was 90℃,the sensitivity was high, and the accuracy could match the analytic request. This experiment detected MTBE at different interval, and found that the result of detection didn't change after30 min. 30 min was the equilibrium time.3. The gas in the headspace bottle was detected by Agilent 6890N/FID GC, the DB-MTBE capillary column was used to separate the samples. Absorbing 500uL gas from headspace bottle by hermetic syringe, and injected into GC. The station of GC was as follows:The procedure heats mode: 35 °C (5min) 15"c/mm > 100°C (2min);FID: 250 °C;H2 flow velocity: 40-45ml/min;Air flow velocity: 400ml/min.This method was single, and easy to operate, the detected limit was 0.2443ug/L. The recovery ratio was measured by standard affiliation method to investigate the accuracy of the method. The adding level was 0.74-3.70mg/kg, and the average recovery ratio was 95-98%. The minimum detectable quantity was 2.02x10 12g. The relative standard deviation was 1.4-4.2%.4. The result of the effect of soil properties on determination showed: different soil fractions from the same kind of soil affected determination dramatically, the difference of the results of different soil fractions was significant or very significant. While the results difference of the same soil fractions from different soil was not significant. So, the composition of soil has little effect on determination. The results difference of lmm soil grain size and fresh soil samples was not significant, ether. So, fresh soil samples could fix amount with by standard curve that came from other kind of soil. When the fresh samples were air-dried, MTBE could not be detected. So the samples were taken back, they should be detected as soon as possible.5. The result of the adsorption kinetics and thermodynamics behavior of MTBE absorbed by black soil in water solution showed that the absorption precession could fit for Banum model. The result of the activation energy of adsorption(Ey), the activation enthalpy of adsorption(AHy), the activation free energy of adsorption, the activation entropy of adsorption(ASy) showed that the absorption precession was a exothermic precession. The adsorption isotherm line of MTBE by black soil in water solution could fit for Freundlich model. There were different degree of difference among the actual measurement and the estimated value of the organic carbon adsorption index (Koc). This was because of difference of test method, temperature, pH of soil, concentration of chemical matter and salinity.6. The result of the concentration of MTBE in soil around Changchun city showed thatmost of the soils in the survey areas were contaminated by MTBE. This survey covered eight sections of Changchun city. The gas stations, both sides of the main roads and the farmland that far away from gas station and main roads were selected to collect soil samples, and there were 80 sites totally. Topsoil of every site was collected and detected. The determination results showed that MTBE could be detected in all the soil samples from gas station and the sides of main roads. And the concentration of MTBE in soil from gas station was times higher than that of soil from the sides of main roads. In summer, the concentration of MTBE in soil was higher than that of spring and autumn, this was primarily because of the effect of air flow and rainfall. In the farmland, trace amount of MTBE was detected by accident. There were no rules of time, site and concentration of MTBE when it emerged in farmland. So it is reputed that MTBE in farmland was affected by weather and human factors and emerged at random. Refer to the pollution criterion of some states in US, the concentration of soils from many sites were overproof. So it is necessary to continue the study of the environmental behavior of MTBE in soil, and educe the transfer and transform law in the underground water-soil-air system.