Salt-assisted Thermal Desorption Treatment Technology Of Mercury-contaminated Soils

Mercury is the only liquid metal under normal temperature, but the production,pollution characteristics, harm and remobilised are very similar, known as the onlykind of heavy metals "remobilised. Mercury contaminated soil samples were collectedfrom Qinghai and Qunnan both chlor-alkali industry factories.Effects of thermaldesorption temperature and residence time on mercury removal efficiency wereanalyzed.At the same time,7kinds of mercury species of the samples in continuousextraction were researched, this paper discussed the changes in different mercuryspecies during the thermal desorption process of concentration change. Discussadding chlorine salt at the same time, with pure thermal desorption treatment underthe same conditions the soil sample, the removal efficiency of mercury, mercurychloride salt is added in the sample form, distribution under the condition of differenttemperature treatment modality.Results show that the thermal desorption method for mercury removal rate ofheavy pollution of mercury in soil and feasibility. Mercury in the soil mainly exist ininorganic form, most of its boiling point below500℃, in the process of desorptionvolatile is very strong, is easy to release to gas phase product. Under the condition ofnormal pressure desorption, removal the total mercury in the soil is the main way totake off the attached temperature reaches the boiling point of mercury compounds.Due to environment security, economy, the best of soil samples collected fromQinghai, Yunnan,thermal desorption temperature and residence time should at300℃and60min,500℃and30min, respectively. The carrier should be used in the air.In chlorine salt added as follows: sodium chloride, magnesium chloride, calciumchloride, tetramethyl ammonium chloride and tetrabutyl ammonium chloride, otherconditions are consistent, adding calcium chloride stripping effect is best. Also foundthat the total samples of yunnan high mercury content, chloride salt synergy strippingefficiency is more obvious. Samples of yunnan, adding calcium chloride, added1%,stripping temperature is400℃, residence time for30min, carrier gas to the air, theremoval efficiency is as high as98.86%, conform to the target value of repair10mg/kg. Has little effect on chlorine salt and add sample in qinghai. Various forms of mercury in hot stripping and chlorine salt synergy stripping all will happen in theprocess of transformation, in the end after treatment of mercury in soil mainly exist inresidue or lattice states, environmental risk is small.