| With the continuous development of social economy,the continuous upgrading of electronic technology,the faster and faster updating of electronic products,and the increasing amount of electronic waste,it has become the fastest growing garbage in the world.Electronic waste is becoming a new source of hazardous waste pollution and has gradually become an important issue affecting China's environmental safety.The disposal of waste circuit boards has become the focus of attention.If it can be properly recycled,it will not only contribute to environmental protection,but also promote the sustainable development of society.The recycling of waste circuit boards is an extremely complicated process.The circuit board is composed of metal part and non-metal part.The non-metal part is mainly epoxy resin and has high content of organic substances.Therefore,they can be used as new raw material for preparing activated carbon.Based on this,this study took the non-metallic part of waste circuit boards as raw material,explored the feasibility of preparing activated carbons from waste circuit boards using a variety of activation methods.Analytical methods such as electron microscope,specific surface area analyzer and fourier transform infrared spectrometer were used to analyze the physical structure and chemical property of activated carbons.Activated carbons were applied to treat different types of wastewater.This research mainly starts from the.following aspects:(1)Since the raw material is the non-metallic part of waste circuit boards,the prior separation technology will directly affect the composition and shape of the raw material.Therefore,the influence of separation technology on the physicochemical properties of waste circuit boards based activated carbon was first studied.Waste circuit boards was pre-treated by crushing magnetic separation and electrostatic separation.The non-metallic parts were selected as raw materials.The effect of separation methods on the specific surface area and pore size structure of pyrolytic carbons prepared from waste circuit boards was examined.By comparison,it was found that activated carbon prepared from the non-metallic part after electrostatic separation has a loW porosity,a specific surface area of 235 m2/g,a low content of surface functional groups,a yield of 43.5%.Activated carbon prepared from the non-metallic part after magnetic separation has a higher porosity,a specific surface area of 313 m/g,a higher content of surface functional groups,and a yield of 41.8%.Therefore,the non-metal part of waste circuit boards after crushing magnetic separation is more suitable as raw material for preparing activated carbon.(2)Using the non-metal part of waste circuit boards after crushing and magnetic separation as raw material and KOH as the activator to prepare activated carbon,the influence of heating methods of traditional heating and microwave heating method on the physicochemical properties of the waste circuit board based activated carbon was investigated,and the impact factors of preparation process were also explored.The optimal preparation conditions were determined,methylene blue was used as an indicator to compare the adsorption performance between two kinds of activated carbon.The results showed that the optimal preparation conditions for carbonization process were as follows:temperature of 600 ? and time of 2 h;the optimal preparation conditions for traditional heating method were as follows:the ratio of agent to material of 3:1,temperature of 800 ? for 1 h;the optimal preparation conditions for microwave heating method were as follows:the ratio of agent to material of 3:1,power of 700 W for 15 min.Activated carbon prepared through traditional heating has a specific surface area of 2590 m2/g,an average pore size of 2.742 nm and a yield of 22.5%.Activated carbon prepared through microwave heating has a specific surface area of 2812 m2/g,an average pore size of 2.143 nm and a yield of 25.9%.Compared with traditional heating method,microwave heating method has high heating speed and uniform heat,activated carbon prepared through microwave heating method has larger specific surface area,lower average pore diameter,more regular pore structure,higher yield,but lower functional group content.At 25 ?,the maximum adsorption capacities of methylene blue for activated carbons prepared through traditional heating and microwave heating method were 737.19 and 692.44 mg/g,respectively.The reason why activated carbon prepared through traditional activated carbon has a lower specific surface area and higher adsorption capacity is due to its higher surface functional group content,there is a hydrogen bonding effect and an electron donor-acceptor interaction between activated carbon and methylene blue molecule,which can promote the adsorption.(3)The effect of activation method on the physicochemical property and adsorption performance of waste circuit boards based activated carbon was studied.Activated carbons were prepared by steam physical activation,NaOH chemical activation and H3PO4-steam physicochemical activation respectively.The influencing factors in the three preparation processes were discussed,and the physicochemical properties of activated carbons prepared by the three activation methods were also compared.In the steam activation method,the effects of carbonization time and temperature on the pore structure of carbonized sample,activation time and temperature on the pore structure of activated carbon were investigated.The results showed that the optimal conditions for steam activation were carbonization time of 2 h,carbonization temperature of 600 ?,activation time of 90 min and activation temperature of 800 ?.Activated carbon has a specific surface area of 804 m/g and a pore volume of 0.492 cm3/g.In the NaOH activation method,the effect of the mixing method of the carbonization sample and the activator on the physicochemical properties of the activated carbon was investigated.The specific surface area of dry-mixing activated carbon can reach 2304 m2/g,the pore volume can reach 1.171 cm3/g,the specific surface area of wet-mixing activated carbon can reach 1141 m2/g,and the pore volume can reach 0.576 cm/g.At 25 ?,the maximum adsorption capacity of ciprofloxacin for dry-mixing activated carbon and wet-mixing activated carbon can reach 572.11 mg/g and 381.29 mg/g,respectively.Therefore,dry-mixing activated carbon show better in physicochemical properties.In the H3PO4-steam activation,the influence of the activation sequence of H3PO4 and steam activation was investigated.The specific surface area,pore volume and adsorption capacity for malachite green of activated carbon prepared by one-step activation were 810 m2/g,0.600 cm3/g and 769.2 mg/g,respectively.The specific surface area,pore volume and adsorption capacity for malachite green of activated carbon prepared by two-step activation were 730 m2/g,0.455 cm3/g and 714.3 mg/g,respectively.Through comparison,it was found that the activated carbon prepared by NaOH dry-mixing have the largest specific surface area,but low yield,and it has severe corrosivity for the instrument.The specific surface area of activated carbon prepared by steam activation and H3PO4-steam two-step activation was higher,but the preparation time was longer.The activated carbon prepared by H3PO4 activation has a higher yield,but the specific surface area and microporosity are lower.The specific surface area,microporosity,and yield of activated carbon prepared by the H3PO4-steam one-step activation are ideal,and the preparation time is short,therefore it is suitable for practical industrial production.(4)Due to the large amount of copper or metal oxides remaining in the non-metal part of waste circuit board after separation,it has a certain impact on the preparation of waste circuit board based activated carbon.Therefore,the non-metal part of the waste circuit board containing no metal component is used as a raw material.Copper powder and copper oxide powder were added during the preparation process to investigate the effects of copper and copper oxide on the properties of waste circuit boards based activated carbon.H3PO4 was used as the activator,the optimal doping amounts of copper powder and copper oxide powder were investigated.The experimental results show that the optimal doping amounts of copper powder and copper oxide powder were 0.15 g and 0.2 g,respectively.The presence of copper and copper oxide increased the specific surface area of the activated carbon,enlarged the average pore size,reduced the yield,enhances adsorption performance and increases surface functional group content.The order of specific surface area was AC/CuO(676 m2/g)>AC/Cu(658 m2/g)>AC(470 m2/g).The order of microporosity was AC(36.32%)>AC/Cu(30.18%)>AC/CuO(29.11%).The order of the average pore size was AC/Cu(3.662 nm)>AC/CuO(3.642 nm)>AC(3.233 nm).The order of yield was AC(36.4%)>AC/Cu(32.7%)>AC/CuO(30.1%).At 20 ?,the adsorption capacities of the three activated carbons for cephalexin were:AC/CuO(86.09 mg/g)>AC/Cu(84.15 mg/g)>AC(66.03 mg/g).The presence of copper and copper oxide promotes the progress of the activation reaction,improves the physicochemical properties of the activated carbon and plays a role in the modification of activated carbon.The study on regeneration of activated carbon found that AC,AC/Cu and AC/CuO cycle rates after the adsorption-regeneration cycle exceeds 60%,indicating that the three activated carbons have a certain value of renewable utilization.In this study,activated carbons were prepared from the non-metallic part of waste circuit boards by different activation methods.The feasibility of preparing waste circuit board based activated carbon and its application in waste water treatment were studied.This study provides a reasonable way for the recycling of waste circuit boards and realizes the recycling of solid waste. |
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