Preparation Of Municipal Sludge Pyrolysis Biochar And Its Adsorption Properties For Ni²⁺

With the gradual increase of municipal sewage treatment volume,the amount of municipal sludge generated is increasing day by day.At the same time,due to the strict requirements of the state on sludge discharge,properly treating and disposing sludge has become a major problem.The traditional sludge treatment and disposal methods,including sludge landfill,incineration,and sludge agricultural use,have great drawbacks.Sludge pyrolysis technology has become a major direction of sludge resource utilization,and has attracted many scholars to study.In recent years,it has been found that biochar prepared by sludge pyrolysis has strong adsorption capacity for heavy metals.On the other hand,Nickel plating technology is widely used in industrial production such as electronics,machinery,and automobile manufacturing because of its superior performance.Then resulting in a large number of nickel-plated wastewater.Nickel-containing wastewater is very harmful,and it's emission standards are becoming more and more strict.However,various existing nickel-containing wastewater treatment methods have their own shortcomings,So it is urgent to find an efficient and inexpensive way to treat nickel-plated wastewater.In this paper,six kinds of primary sludge biochar and six kinds of sludge biochar activated by ZnCl₂ were prepared by pyrolysis method at the final temperature of300⁸00??set a test condition every 100??,respectively recorded as SBC and A-SBC,the biochar produced at each specific temperature is recorded as SBC-XXX or A-SBC-XXX?xxx indicates specific temperature?;Calculating the yield of biochar produced at different temperatures;determining the iodine value and methylene blue value of SBC and A-SBC to characterize their basic adsorption properties;and scanning electron microscopy?SEM?,infrared spectroscopy?FTIR?and N₂ adsorption-desorption were used to characterize its surface morphology,surface group and specific surface area.Finally,the adsorption properties of SBC and A-SBC on Ni²⁺ions in solution were investigated.The initial pH of the solution,the amount of biochar and the initial Ni²⁺ion concentration were used as the variable factors to investigate the optimal conditions for the adsorption of Ni²⁺ions by SBC and A-SBC.The main research conclusion obtained are as follows:?1?Through the pyrolysis preparation experiments of SBC and A-SBC,the yields of SBC and A-SBC obtained by pyrolysis at 300⁸00?were between 45%⁷0%and35⁹0%,respectively,which were higher than the yield of general agriculture and forestry waste?25%³5%?.The biochar yields of both SBC and A-SBC showed a tendency to decrease with increasing temperature.The biochar yield of SBC dropped the fastest at 300⁴00?,mainly due to water precipitation and a large amount of mass cellulose in the sludge being pyrolyzed as volatile compounds in this temperature range,and it is finally maintained at around 50%.The yield of A-SBC decreased the fastest at 500⁶00?,mainly due to the dehydroxylation and dehydration of the carbon structure under the chemical catalysis of ZnCl₂,which promoted the volatilization of more compounds in the sludge,but after 600?The decline is slower.Between 300 and580?,the yield of A-SBC is much higher than that of SBC,and the yield of A-SBC is lower than SBC after 580?.?2?The iodine value and methylene blue value of SBC and A-SBC increased first and then decreased with the increase of pyrolysis temperature.The iodine value of SBC reached the maximum value of 1002.51 mg/g at 400?,and the methylene blue value reached the maximum value of 17.62 mg/g at 700?.The iodine value of A-SBC reached a maximum value of 1111.644 mg/g at 500?,and the methylene blue value reached a maximum value of 20.09 mg/g at 400?.The pyrolysis process is insufficient and the pores are not developed when the pyrolysis temperature is too low.But if the temperature is too high,sintering will occurs in the sludge,and the pore structure will be destroyed.ZnCl₂ performs pore activation at 400?or higher temperature.Compared with the iodine value of SBC and A-SBC,the difference is the largest at 500?,A-SBC is1.48 times iodine value of SBC,and the difference is not obvious at other temperatures.It shows that ZnCl₂ has the best activation at 500?.?3?According to the adsorption experiments of Ni²⁺ions by SBC and A-SBC,combined with characterization and comprehensive comparison,it can be found that SBC and A-SBC have good adsorption properties for Ni²⁺ions,especially A-SBC activated by ZnCl_2.The pore structure of A-SBC is developed,the content of hydroxyl?-OH?and carboxyl?C=O?functional groups is more abundant,and the adsorption performance is greatly improved,the saturated adsorption capacity was increased from28.33 mg/g?SBC?to 62.57mg/g?A-SBC?.SBC-700 has the best adsorption performance for Ni²⁺in the six unactivated sludge biochars.When the initial pH of the solution is 8and the dosage of biochar is 75 mg?The concentration is 2.5g/L?,SBC-700 has the best adsorption capacity for Ni²⁺ions,and the removal rate of Ni²⁺ions is 86.8%,which has little difference with commercial activated carbon?coconut?under this condition?86.05%?.A-SBC-500 has the best adsorption performance for Ni²⁺in the six sludge biochars activated by ZnCl₂.When the initial pH of the solution is 7 and the dosage of biochar is 75 mg?The concentration is 2.5g/L?,the adsorption capacity of A-SBC-500 for Ni²⁺is the best,and the removal rate of Ni²⁺is 96.5%,which is better than that of commercial activated carbon?coconut?under this condition?77.11%?.