Study On The Remediation Effect Of Compound Stabilizer On Heavy Metal Contaminated Sediment

With the development of urbanization and industrialization as well as the increasing of agricultural activities,the discharge of industrial wastewater and domestic sewage leads to increasingly serious heavy metal pollution in sediment.Heavy metals are highly toxic,persistent,non-biodegradable,and cumulative.They exist in the sediment for a long time and eventually pose a potential threat to human health and ecosystem through the food chain.Therefore,heavy metal pollution has caused widespread public concern,and many in-situ remediation technologies?such as capping,dredging,electrokinetic extraction,chemical washing,phytoremediation,stabilization,etc.?have been adopted to deal with the heavy metal pollution problem.Among them,stabilization is an important in-situ repair technique,which has been widely concerned due to its fast repair,low cost and high efficiency,and simple operation.At present,there have been more studies on the stabilization of single or the same type of composite heavy metal polluted sediments.Existing studies have given little consideration to the coexistence of heavy metals and arsenic.Most cationic heavy metals and arsenic have different properties and inconsistent responses to stabilizers,making it difficult to repair arsenic-containing composite heavy metals contaminated sediment.Many stabilizers have a good treatment effect on a single heavy metal,but the complex pollution characteristics of multiple heavy metals combined pollution will increase the difficulty of pollution repair.It is difficult to achieve the simultaneous repair of multiple heavy metals with a single stabilizer,and the composite stabilizer can pass.The advantages complement each other,make up for the deficiencies of each component,and can meet the requirements of the treatment of composite heavy metal polluted sediments.Therefore,it is very important to repair multiple heavy metal contaminated sediments with a certain proportion of multiple stabilizers.In this paper,Copper?Cu?,Zinc?Zn?,Lead?Pb?,Cadmium?Cd?,and Arsenic?As?compound polluted sediments are used as research objects.Selection of iron-containing materials?Ferrous Sulfate-FeSO₄,Iron Powder-Fe,Iron Chloride-FeCl₃?,alkaline substances?Magnesium Oxide-MgO,Calcium Oxide-CaO,Calcium Carbonate-CaCO₃?and clay minerals(Kaolin-Kaolin,?Bentonite-Bentonite,Montmorillonite-Montmorillonite?3 types,a total of 9kinds of stabilizers to stabilize the composite polluted sediment,according to the leaching concentration of stability,selection of 3 types of 3 kinds of stabilizers,and then use the response surface optimization experiments to obtain the optimal ratio;discuss the factors affecting the stabilization effect such as water content,dosage,dosage method,interval time and stabilization time;use The acetic acid buffer solution method was used for toxic leaching and modified BCR morphological extraction method to analyze the leaching concentration and morphology of heavy metals before and after stabilization to evaluate the effect of composite stabilizer repair.Experimental results show that:?1?The occurrence state and pollution characteristics of heavy metals show that the five kinds of heavy metals in the test sediment are all high in content,and the occurrence forms are mainly acid-extractable,reducible and oxidizable states and other non-residue states.The low proportion of the state indicates that heavy metals have high bio-mobility and bio-availability,and are more harmful to the environment.?2?Stabilizer screening experiments show that alkaline substances and clay minerals can effectively stabilize the five heavy metals in the sediment.Among them,the stabilizing effect of alkaline substances is positively correlated with the dosage,and different stabilizers have certain effects on different heavy metal elements.Selectivity.The stability rate of MgO to Cu,Zn,Pb,Cd,and As is higher when the dosage is 10%,respectively 83.20%,56.45%,89.71%,46.48%,55.96%;Kaolin is 5 The stability rates for Cu,Zn,Pb,Cd,and As at 34%are 34.26%,24.91%,13.79%,13.97%,and 38.49%respectively;the stability rate of As for FeSO₄ at a Fe/As molar ratio of 9 is 87.78%,however,Cu,Zn,Pb,and Cd were activated under this dosage.?3?Through single factor experiments,the FeSO₄ dosage in the BBD design is Fe/As=9,the MgO dosage is 10%and the Kaolin dosage is 5%,which provides a basis for the response level method to provide factor level selection.?4?Response surface method optimization experiments show that the interaction strength and change trend of the stabilizing effects on the five heavy metal elements when the three stabilizers act simultaneously are different.The increased dosage of FeSO4 is conducive to the stability of As.The increased dosage of MgO and Kaolin is conducive to the stability of Pb,Cu,Zn and Cd,while FeSO₄ plays the opposite role.?5?The optimal ratio obtained by the response surface method is:FeSO₄ dosage is 9.76Fe/As molar ratio,MgO and Kaolin dosage is 11.07%and 5.95%of the sediment quality,verification test shows that Cu,Zn,Pb The stabilization efficiency of Cd,As is 85.98%,83.71%,83.57%,73.25%and 88.81%,which is very close to the stability rate of each heavy metal under the optimal conditions predicted by the regression model,indicating that the experimental value and the predicted value fit Higher,indicating that the model has higher reliability and better prediction of the experiment.?6?Study the influencing factors to obtain the optimal conditions:the optimal moisture content is 30%,the total dosage of the composite stabilizer is the optimal ratio,the dosage method is to first add FeSO₄,then MgO and finally Kaolin,stable the step-by-step addition interval of the agent is 7d,and the stability rates of Cu,Zn,Pb,Cd,and As reached 63.81%,97.09%,94.73%,83.9%,and 99.31%respectively after being stabilized under this condition for 63d.Heavy metal contaminated sediment has a good stabilizing effect.?7?The analysis of leaching toxicity showed that:using acetic acid buffer solution to extract the bottom mud,the order of heavy metal leaching concentration is stable before bottom mud>>stable after bottom mud,indicating that the compound stabilizer can effectively reduce the heavy metal in bottom mud The leaching concentration and effective stabilization of heavy metals in the sediment,of which Cu,Zn,Pb,and As have reached reach the limit of<Standard for Pollution Control on the Landfill Site of Municipal Solid Waste>?GB16889-2008?.,and the stability rate is all above 85%.?8?Occurrence morphology analysis showed that after the composite stabilizer was stabilized for 63 days,the five heavy metals in the sediment changed from the highly active acid extractable state to the less active oxidizable and reducible state and the lowest residue state Transformation,in which the acid extractable states of Cu,Zn,Pb,Cd and As decreased by 19.30%,52.73%,5.11%,34.05%and 34.44%,respectively,and the residue state increased by 28.61%,33.53%,19.56%,35.19%,20.17%,indicating that the composite stabilizer can effectively reduce the migration and bioavailability of heavy metals.