The Degradation Of Organic Pollutants By Steel Slag-based Fenton-like Reactions And The Mechanism Study

With the rapid development of modern industrialization,environmental pollution is becoming more and more serious.Among them,organic pollutants such as pesticides and antibiotics pose a great threat to the ecolo gical environment and human health.It is an urgent task to seek efficient,simple and low-cost removal methods.China is the world's largest producer of steel,and also produced a lot of steel slag.Steel slag contains Fe₂O₃ and FeO,therefore it can be used as a catalyst for Fenton-like reaction.However,slag also contains a large amount of alkaline components?CaO and MgO,etc.?,which will cause the rapid increase of soultion pH,negatively impact the Fenton reaction.Therefore,high amout of acid are requied to maintain the acidic condition for slag catalyzed Fenton-like reaction,which makes the process complex and uneconomical.In order to solve the above problems,we used chemical treatment to modify the steel slag,reduced the alkalinity and significantly improved the catalytic ability of slag.On the one hand,the profermance of modified-steel slag/H₂O₂ Fenton-like systems for the removal of organic pollutants from waste water was studied.On the other hand,we investigated the feasibility of application of steel slag for remedation of pesticide contaminated soil.The performance of slag/H₂O₂ Fenton-like system and the combined combined chemical and biological treatment?slag/H₂O₂ combined with straw/phanerochaete chrysosporium?along with the effects of the treatments on soil properties were studied.The specific research work and achievements of this paper include the following five parts:The first section described an affordable and effective heterogeneous Fenton-like process.Preparation and utilization of an iron-rich catalyst,salicylic acid–methanol?SAM?modified steel converter slag?SCS?,were investigated for the degradation of alachlor in wastewater.Means of characterization methods were used to assess the morphology and crystal structure of the prepared catalysts.Results showed that SAM modification can selectively remove calcium silicate minerals from surface of SCS.The modification decreased the alkalinity of SCS and led to a prominent decrease in the specific surface areas and iron content,which dramatically improved the catalytic property of SCS.The removal rate of alachlor at initial pH 3.0 in SAM-SCS/H₂O₂system was 3.07 times of that in SCS/H₂O₂ system.Further studies showed that this heterogeneous Fenton-like process was more suitable to be performed at relative higher temperature?30-40°C?and lower initial pH?2.0-3.0?.A small decrease?2.1%?was found in the activity of SAM-modified SCS after four runs,indicating that SAM-SCS has good stability during the process.The second section studied the degradation of rhamnolipid-solubilized hexadecane by salicylic acid-methanol?SAM?modified-steel converter slag?SCS?catalyzed Fenton-like process.Compared to SCS,SAM-SCS exhibited better adsorption performance and the maximum adsorption capacities of hexadecane and rhamnolipid were about 0.23 and 0.28 mg g^-1,respectively.Up to 81.1%of hexadecane removal was achieved within 24 h,whereas only 36%of rhamnolipid was degraded.And the blocking effect of high concentration of rhamnolipid was observed during the degradation process.More importantly,we found that SAM modification could effectively reduce the alkalinity of SCS,which made pH value of solution maintain 6.0-6.72 during oxidation reaction.All these showed that SAM-SCS/H₂O₂Fenton-like process could be a cost-effective and promising approach for treatment of surfactant-solubilized hydrophobic organic compounds.In the third section,a novel composite Fe/Co catalyst was synthesized via the modification of steel converter slag?SCS?by salicylic acid–methanol?SAM?and cobalt nitrate?Co?NO₃?₂?.The results indicated that the Co-SAM-SCS/H₂O₂Fenton-like system was very effective for sulfamethazine?SMZ?degradation at a wide pH range.At initial pH of 7.0,the degradation rate of SMZ in Co-SAM-SCS/H₂O₂ system was 2.48,3.20,6.18,and 16.21 times of that in Fe-SAM-SCS/H₂O₂,SAM-SCS/H₂O₂,Co?NO₃?₂/H₂O₂ and SCS/H₂O₂ system,respectively.The preliminary analysis suggested that high surface area of Co-SAM-SCS sample and synergistic effect between introduced Co and SAM-SCS are responsible for the efficient catalytic activity.During the degradatio n,three main intermediates were identified by high performance liquid chromatography–mass spectrometry?HPLC–MS?analysis.Based on this,a possible degradation pathway was proposed.The studied Fenton-like process also showed high degradation of SMZ in river water and municipal wastewater.In section four,the remediation of atrazine contaminated soil with steel converter slag?SCS?catalyzed Fenton-like process was reported.The effects of various operating parameters,such as SCS loads and H₂O₂ concentrations were evaluated with respect to the removal efficiency of atrazine.Results show the optimal SCS load and H₂O₂ concentration were 80 g kg^-1 and 10%,respectably.The graded modified Fenton's oxidation with a 3-time addition of 10%H₂O₂ was able to remove 93.7%of total atrazine in the contaminated soil and maintain soil temperature within 50°C.In contrast to traditional Fenton treatment,a slight pH increase has been observed due to the addition of SCS.After the treatment,dissolved organic carbon?DOC?content increased to 1.206 g kg^-1 from an initial value of 0.339 g kg^-1.More importantly,experiment conducted at natural conditions with SCS gave the similar atrazine removal to the experiments with the other catalysts?e.g.,Fe _SO₄ and Fe₂O₃?.In section five,on the basis of section four,a combined chemical and biological treatment?slag/H₂O₂ combined with straw/phanerochaete chrysosporium?was proposed for the treatment of atrazine contaminated soil.It was found that the removal rate of atrazine by the combined treatment was higher than the sum of the single chemical treatment and biological treatment.Further study showed that the optimal amount of straw and SCS was 90 g kg^-1 and 50 g kg^-1,respectively,under this condition,this combined treatment can remove about 90%of atrazine.The study also found that the pretreatment of Fenton-like chemical oxidation could promote the secretion of enzymes from phanerochaete chrysosporium,and thus improve the degradation of atrazine.