两步煅烧法回收芬顿污泥

Recovering Fenton sludge by two-step calcination process

以芬顿污泥为原料,采用两步煅烧法通过氧化还原作用制备四氧化三铁将铁泥回收。结果表明:污泥中铁元素的转变顺序为羟基氧化铁→氧化铁→四氧化三铁→氧化亚铁→铁单质。芬顿污泥中铁元素主要以羟基氧化铁的形式存在,在第一步400℃煅烧3 h以后,污泥主要成分为氧化铁。在第二步煅烧中,铁的存在形式与加入碳粉后的反应温度关系密切,700℃污泥中的铁主要是以四氧化三铁的形式存在,此时用磁选技术即可将具有磁性的四氧化三铁分离出来,此技术在工艺流程中没有产生废水、危废等物质,过程中的主要材料污泥与碳粉原料简单且完全可回收,减少了二次污染,此技术在工业水处理领域有很好的应用前景。

Background,aim,and scope Fenton oxidation technology is characterized by high efficiency,low cost and hardly any selectivity.As an Advanced Oxidation Process(AOP),Fenton oxidation method has been widely used in the field of toxic and refractory industrial wastewater.However,it is inevitable to produce a large amount of iron-containing sludge in the process of wastewater treatment.The iron-containing sludge has not been well treated and is now treated as hazardous waste because of the low reuse value.So far,there have been few studies on iron-containing sludge treatment.In order to solve the problem,we explored a method to deal with the iron-containing sludge generated by Fenton reaction in this paper,so as to reduce the harm of sludge to the environment and the cost of transportation and disposal as hazardous waste.Materials and methods The iron-containing sludge generated by Fenton reaction was used as a feedstock during the experiment in this paper.Firstly,0.1 g of freeze-dried sludge was put into a muffle oven.The calcination temperature was set from 100℃to 200℃,300℃,400℃and 500℃.The calcination time was set to 1 h,2 h,3 h,4 h and 5 h at different calcination temperatures,respectively.The thermogravimetric and XRD analysis were employed to investigate the effects of calcination temperature and time on the physicochemical properties of Fenton sludge.Secondly,the sludge after calcining in the first step was mixed with the carbon powder according to the mass ratio of 84∶16.And then the mixture was calcined in a tube furnace from 400℃to 900℃for 2 h,respectively.The changes of iron phase composition were analyzed by XRD in the calcination process.Results The experimental results show that the transformation order of iron element in the Fenton sludge was FeOOH→Fe_(2)O_(3)→Fe_(3)O_(4)→FeO→Fe at different calcination temperatures.The iron element in original Fenton sludge mainly existed in the form of FeOOH.While the main component was Fe_(2)O_(3) after the Fenton sludge was calcined at 400℃for 3 h in the first stage of calcination.The iron element mainly existed in the form of Fe_(3)O_(4) at 700℃and FeO at 800℃in the second stage of calcination.The elemental iron was further produced at 900℃.Discussion The existing form of iron did not change with the increase of calcination temperature during the first stage of calcination.It could be that the remaining organic matter has been completely carbonized.The existing form of iron was related to the reaction temperature when the carbon powder was added to the mixture in the second stage of calcination.At this point,magnetic separation technology can be used to separate Fe_(3)O_(4) from the residue,realizing the resource utilization of the Fenton sludge.The following three points need to be further studied:(1)Is it easier to find the relationship between the form of iron and the temperature if the temperature gradient is shortened?(2)The reaction mechanism is complex and needs further study.(3)It is necessary to find the temperature at which the iron compound is completely converted to zero valence iron.Conclusions A two-step calcination method was used to study the existing form of iron in Fenton sludge in this paper.The main components of the Fenton sludge were hydroxyl oxidize iron,organic compounds and some inorganic salts.Then the Fenton sludge was used as raw material and calcined at 400℃for 3 h in muffle furnace.It was found that the organic matter in Fenton sludge had been completely oxidized by XRD and TG analysis,while the existing form of iron in the residue was ferric oxide.After the first stage of calcination,the residue mixed with carbon powder was taken as raw material,and further calcined in a tubular furnace.The mixture was calcined at 700℃for 2 h,the iron in the residue basically existed in the form of ferroferric oxide.At this point,magnetic separation technology can be used to separate ferroferric oxide from the residue,so as to realize the resource utilization of the Fenton sludge.Recommendations and perspectives No waste water,hazardous waste and other substances are produced in the two-step calcination process of Fenton sludge,which reduces secondary pollution,and the iron element in Fenton sludge can be completely recycled.Therefore,this technology has a broad application prospect in the field of industrial water treatment.