| The sediment concentration of rivers in China is generally high,and the proportion of cohesive fine sediments is relatively large.Due to its large specific surface area,cohesive fine sediment are prone to absorb different kinds of trace metals and organic compounds in the natural water body,making the flocculation aggravate or weaken.Therefore,the process can change the physicochemical characteristics and mechanism of sediment movement.Hence,carrying out the mechanism of sediment movement under the influence of water quality characteristics is of positive significance for promoting the development of the theory of sediment movement mechanics.The project selected LAS(sodium dodecyl benzene sulfonate),CATB(cetyl trimethyl ammonium bromide)which belong to typical anions and cationic surfactants respectively as the research objects.The effects of different ionic surfactants on the surface charge distribution and flocculation degree of sediment were analyzed by studying the adsorption and desorption equilibrium of surfactant in water and sediment under different sediment particle sizes and water body temperature.By means of the Griffith tube and the settling equipment,We tried to explore the law and mechanism of different type of ionic surfactants on sediment hydrostatic settling behavior of different grain size groups.Through dynamic flume test,the starting current velocity and deposition velocity of sediment after surfactant adsorption was studied under different hydrodynamic factors.The main research results include the following aspects:(1)Based on the capillary electrophoresis instrument,a highly efficient and rapid method for the detection of anionic surfactant LAS and cationic surfactant CTAB in water was established.The results showed that under the optimized experimental conditions,the LAS content in water can be determined without pretreatment within 20 minutes.The linear range is 0.5 mg/L~10 mg/L can detect CTAB content in water within 10 min,with a linear range of 0.5 mg/L~6 mg/L.Compared with the traditional method,this method not only improves the sensitivity but also reduces the detection time.,and the sample volume decreased from 200 m L to 1m L.(2)The adsorption kinetics of the surfactant on the sediment surface under different conditions was analyzed and compared.The results showed that the adsorption of cationic surfactant CTAB on the sediment surface was two orders of magnitude higher than that of the anionic surfactant LAS,and it showed that The temperature rises,the adsorption rate increases,and the saturated adsorption decreases.The pH value had no obvious effect on the adsorption rate of LAS and CTAB,but with the increase of p H value,the saturated adsorption capacity of anionic surfactant LAS increased and that of cationic surfactant CTAB decreased.(3)The adsorption thermodynamics of the surfactant on the sediment surface were analyzed and compared.The results showed that the adsorption isotherm of the anionic surfactant LAS was L-type.The main manifestation was physical adsorption.The adsorption isotherm of the cationic surfactant CTAB.S-type;LAS,CTAB adsorption isotherms are in line with Langmuir adsorption mode,the correlation coefficient is above 0.9.(4)A test device was set up to simulate the influence of external pollutants on the start and sedimentation of sediment.The results showed that the flow is kept at a constant flow at different flow rates,and the drag force of the water received by the sediment is the same;the principle of the connected vessel and the main body of the gutter are used in the sampling window.Connected,the sampling process does not disturb the water flow patterns.(5)The sedimentation rule under the turbulence of water body was studied with the aid of sediment dynamics simulation device.The results showed that under static water conditions,the sedimentation velocity of sediment decreased slightly with the increase of LAS concentration,and it increased with the increase of CTAB concentration.The Zeta potential is consistent with the change of concentration.Under a flow rate of less than 30 cm/s,the average sedimentation velocity of the moving water is about 0.007 cm/s,and when the flow rate is greater than or equal to 30 cm/s,sedimentation of the water body no longer occurs.The sedimentation velocity of sediment decreases with the increase of LAS concentration,and increases with the increase of CTAB concentration.Under the conditions of water turbulence,the sedimentation velocity of sediment is less than that of hydrostatic sedimentation.(6)With the help of the recirculating water tank,the sediment initiation mechanism under different sediment concentration and surfactant concentration was studied.The results showed that the sediment start flow velocity was between 13 cm/s~20 cm/s,and the surfactant was present.The viscosity coefficient of the sediment surface is increased,the starting drag force is increased,the critical starting velocity of the sediment is increased,but the full starting flow rate is constant,and the effect of the cationic surfactant CTAB on the sediment starting velocity is greater than that of the anionic surfactant LAS.In this dissertation,the influence of surfactants on sediment initiation and sedimentation was systematically studied and analyzed.A capillary electrophoresis instrument was used to detect ion surfactants and a new experiment was conducted to simulate the effect of sediment transport on exogenous pollutants.The device not only provides a theoretical basis for studying the relationship between surfactant and sediment,but also establishes a research method for the effect of pollutants on sediment. |
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