Analytical Method, Sorption And Leaching Behavior Of Typical Quaternary Ammonium Compounds

With the increase of mining activities around the world, numerous pollutants such as flotationreagents have been inevitably released into environment and accordingly caused various ecologicalissues. At present, most of the papers about mining pollutants focused on heavy metals. Variousflotation reagents such as quaternary ammonium compounds (QACs), have been knownextensively used in mining areas to separate, extract or collect the valuable minerals. In many casesthe usage amount of flotation reagents can be very vast, and the consumption amount was expectedto increase in the future. However, very few research has reported about the environmentalbehaviors and ecological risk on pollution caused by the QACs used in mining. The objectives ofthis study are to develop the analytical methods for the simultaneous extraction and determinationof three QAC compunds (dodecyl trimethyl ammonium chloride (DTAC), cetyl trimethylammonium bromide (CTAB) and didecyl dimethyl ammonium chloride (DDAC)) in water and soilsamples. In addition, sorption behavior and migration of QACs on different soils/sediments wereinvestigated by sorption and leaching experiments, respectively. The results would be veryimportant for evaluating the environmental fate and ecological risk of QACs as well as for soilcontamination remediation. The main results were as follows:An analytical method was developed for the simultaneous extraction and determination ofthree QAC compounds in water samples using liquid-liquid extraction and gas chromatographyequiped with mass spectrometry (GC-MS). The qualitative and quantitative analysis of the threeanalytes (DTAC, CTAB and DDAC) were conducted by EI Mass spectra and selected ionmonioring (SIM). In the optimized extraction method, pH and salinity of water sample was adjustedto1.5and3%using hydrochloric acid and sodium chloride, respectively. Then the processed watersample was extracted by chloroform twice with5mL each time in a125mL separatory funnel.Good linear relationships of all the three analytes were obtained in the range of0.01~2mg/L. Thelimits of detection (LOD, S/N=3) was2.5~8.5μg/L. The method was used to analyse real watersamples collected from running water, lake water, river water and beneficiation water. Results ofdetermination displayed the concerntrations of the three analytes in real water samples ranged from 0.06mg/L to2.45mg/L, and their recoveries of spiked standard ranged from65%to113%withrelative standard deviations (RSD)3.8%~23%.An analytical method was developed for the simultaneous extraction and determination ofthree QAC compounds in soil samples using ultrasonic extraction and GC-MS. In the optimizedextraction method, treated methanol (pH value:1.5; LAS concentration:40μg/L) as extractantshowed the highest extraction effeciency compared with other solvents or at other conditions. Soilsample was extracted by ultrasonic extraction method twice with20min and10mL of treatedmethanol each time. The extract of soil sample was purified by neutral alumina column with4cmin length and1cm in diameter, and then was determineted by GC-MS. Good linear relationships ofall the three analytes were obtained in the range of0.02~2mg/L. The LOD (S/N=3) was1.2~4.5μg/kg. The method was used to analyse real soil samples including paddy soil, lateritic red soil, andore tailings collected from a mining district in south China. Results of determination exhibited thatthe concerntrations of the three analytes in real soil samples ranged from0.24to0.41mg/kg, andtheir recoveries ranged from76%to113%with RSD1.1%~12.9%.Sorption kinetics, isotherm and mechanism of QACs on adsorbent were investigated usingbatch sorption experiments. Results showed that sorption of QACs to the paddy soil quicklyreached equilibrium (within60min), and sorption kinetics followed pseudo-second-order kinetics.Sorption process of DTAC, CTAB and DDAC on the paddy soil can be divided into three stages,namely fast sorption stage (within30min), slowly sorption stage (30to60min) and equilibriumsorption stage (more than60min). Adsorption capacity for DTAC, CTAB and DDAC on paddy soildecreased in the order of DDAC> CTAB> DTAC. Both Freundlich model and Langmuir modelfitted well with DTAC isotherm data. DTAC sorption displayed a monolayer sorption process.Sorption of DTAC depended on the exchangeable cations on the surface of clay minerals insoils/sediments, and the functional groups of organic matter in soils/sediments. Soil-water partitioncoefficient (Kd) values of DTAC sorption were positively correlated with clay contents ofsoils/sediments, indicating a higher mobility and ecological risk of DTAC in those soils/sedimentswith low clay contents. XRD analysis showed that QACs was adsorbed on the mineral surface ofsoils/sediments instead of intercalation into their interlayer space. FTIR spectroscopy analysisexhibited that physical sorption or chemical sorption occurred in QACs sorption process for all thetested soils/sediments. Column-leaching test showed that the highest leaching rates and outflows of three QACs wasDDAC, followed by CTAB, further indicated that migration of DDAC in soil is strong and DTACis weak. Correlation analysis showed that a significant negative correlation existed among leachingrates, outflows and carbon chains. Furthermore, peak concentration corresponding translocationdistance of the QACs increased with pH of leaching solution increasing, higher peak concentrationsand higher concentrations in deeper soil of QACs were observed using water at lower pH value (=3)other than using higher pH value (=6) leaching. Moreover, The higher the soil organic mattercontent, the weaker the migration of QACs in soil.