Research On Treatment Of Cyanide Contaminated Soil And Organic Wastewater By Persulfate And Its Activation Technology

In recent years,with the accelerating urbanization process in China,a large number of contaminated sites have emergenced in the city or its surroundings for the further implementation of “suppress the second industry and develop the third industry” and “Industry shall retreat from the urban area and shift to industry zones”,which has become a big challenge for environmentalists to remediate.Among the present remediation technologies,chemical oxidation technology has received great attention for its high efficiency,low selectivity,and so on.What’s more,persulfate and its activation technology are more favored by researchers for their high utilization,environment-friendly,safe and stable,and so on.Activated persulfate is one of the most promising advanced oxidation technology with more powerful oxidizing power which based on generated sulfate radical（SO₄^-·）.Accordingly,this paper utilized persulfate and its activation technology remediated the two types of carrier pollutants in contaminated sites: cyanide contaminated soil and organic wastewater.Meanwhile the feasibility,dynamic characteristics,degradation of pollutants,the development of new activation technology and the activation mechanism has been further studied.The main contents and conclusions are stated as follows:（1）The feasibility study results from the treatment of cyanide contaminated soil by persulfate shown that persulfate could efficiently reduce the cyanide in the soil,and with increasing of the dosage of persulfate the cyanide gradually reduce;Meanwhile,the study of qualitative analysis of cyanide oxidation products indicated that the oxidation product was CO2 and NH3 with less environmental pollution,and the specific reaction mechanism may be as follows: CN-+S2O82-+H2O→CO²⁺NH3+SO42-.Based on the results,it can be known that the chemical oxidation technology of persulfate is feasible and has potential value in engineering application.（2）The transformation process of the easily release cyanide and the total cyanide were researched during the treatment of cyanide contaminated soil by persulfate,the results showed that the total cyanide decreased with the increase of persulfate,the easily release cyanide was up and down but gradually reduced in general.In the soil,the sequence of oxidation of cyanide follows the order: free cyanide,low stable cyanide,moderately stable cyanide,stable cyanide,and high stability of cyanide.During the process of oxidation,the transformation from stable cyanide to low stable cyanide resulted in the increase of the easily release cyanide.The oxidation reaction of the cyanide is the first order kinetic reaction,when the dosage of persulfate increased from 0.290 to 0.870 mmol,the reaction rate constant increased from 3.4×10-4 to 24.5×10-4 min-1.（3）Fe²⁺ activation,thermal activation,Fe⁰ activation,alkali activation persulfate technology has used to deal with cyanide contaminated soil.The results showed that the treatment effect could be improved obviously in the range of activation condition.Among them,the Fe²⁺ activation and thermal activation is more obvious,the removal efficiency of cyanide could be increased by 15.0% and 13.8% respectively compared with the single persulfate.Thermal activation in low permeability soil has some limitations and high energy consumption,so the Fe²⁺ activation was selected to expand further study in the subsequent studies.（4）The orthogonal experiment was designed with four factors to study the optimum conditions for the treatment of cyanide contaminated soils by Fe²⁺ activation,the results showed that the importance follows the order: dosage of persulfate,Fe²⁺ dosage,reaction time and shaking speed.The optimum conditions for 5.0 g cyanide contaminated soil was: 1.160 mmol persulfate,0.014 mmol Fe²⁺,the reaction time was 1 h,shaking speed 100 rpm.And the kinetics of the reaction of cyanide in the soil under the optimum conditions of Fe²⁺ activation persulfate was also studied,the results showed that the reaction of cyanide in soil with Fe²⁺ activation also is the first order kinetic reaction and treatment effect was much better than the single persulfate.（5）The degradation process of iron carbon micro electrolysis activated persulfate system（Ps-Fe/C）,iron carbon micro electrolysis system（Fe/C）and persulfate system（Ps）were firstly compared in the study of the degradation of Rhodamine B（RhB）wastewater,the results showed that the Ps-Fe/C system was feasible and effective to deal with RhB wastewater,and the synergistic effect of iron carbon micro electrolysis and persulfate was obvious.The synergistic action of strong oxidation and activation of the formation of SO₄^-· was closely related to the activation,the possible mechanism was mainly Fe²⁺ activation,Fe⁰ activation,activated carbon activation,acid activation,H2O2/persulfate binary activation system and so on.Secondly,the optimum conditions of the treatment of RhB wastewater（0.2 mM RhB 100 mL）by Ps-Fe/C system was: 10 mM persulfate,0.05 g iron,0.25 g activated carbon.In addition,the results also showed that iron was the key control factor of the degradation of RhB,and activated carbon was the key control factor of the removal efficiency of TOC（Total Organic Carbon）.In this paper,the research on the treatment of cyanide contaminated soil by persulfates and its activation was put forward,which not only enrich the soil cyanide treatment technology,but also provide some reference for the scale engineering application;At the same time the study of the iron carbon micro electrolysis activated persulfate not only develops a new persulfate activation method,but also provides a new industrial water treatment technology.The research results are helpful to persulfate and its activation technology further promotion,as well as provide some preliminary reference for the engineering application.