| How to remove humic acid from micro-polluted water efficiently is a research hotspot in drinking water treatment. On the basis of having developed a composite adsorbent of magnetic carbon nanotubes material coated calcium carbonate with effective adsorption of humic acid, regeneration was applied to this adsorbent after having adsorbing humic acid to save water treatment costs and reduce the amount of sludge. Effect of NaOH solution, chemical oxidation, ultrasonic, microwave as well as ultrasonic pretreated microwave on regeneration of this adsorbent was studied. The influence laws of various factors of all these regeneration methods on regeneration were investigated. The conditions of ultrasonic pretreated microwave method were optimized. The morphology and structure of magnetic carbon nanotubes coated calcium before adsorbing humic acid and after regeneration were characterized. The mechanism of this regeneration approach was investigated, too.The influence law of NaOH solution on the adsorbent regeneration was studied. Effect of factors such as pH, reaction time, temperature, stirring speed and adsorbent concentration on regeneration was investigated. The results showed that regeneration efficiency increased as the pH value increased gradually. When pH was 12, the regeneration efficiency reached 97.57% and good regeneration effect was achieved. Regeneration efficiency showed slight upward trend with the increase of reaction time or reaction temperature. When the stirring speed increased from 200r/min to 400r/min, the regeneration efficiency gradually went up to the highest, and then decreased with the increase of stirring speed. When the adsorbent concentration was less than 5g/L, the regeneration efficiency remained at 95%. But when the adsorbent concentration was higher than 5g/L, a sharp decline appeared in the regeneration efficiency.Potassium persulfate and hydrogen peroxide were used to regenerate the adsorbent. At pH of 12 and the oxidant concentration less than 0.5mmol/L, the potassium persulfate solution had good regeneration effect on adsorbent. But at concentrations higher than 0.5mmol/L, the regeneration efficiency continued to decline with the increasing potassium persulfate concentration. The hydrogen peroxide at different concentrations had no obvious effect on regeneration.The effect of ultrasound on regeneration of the adsorbent was researched. The influence law of factors including ultrasonic power, ultrasonic time, reaction temperature, ultrasonic frequency and pH value on regeneration was probed. The results showed that only when solution was alkaline that ultrasonic was beneficial to regeneration. But the regeneration effect was not obvious. Effect of ultrasonic power and ultrasonic temperature on regeneration was little. With the increase of ultrasonic time and ultrasonic frequency, the regeneration effect increased slightly. When oxidant of hydrogen peroxide, potassium permanganate or sodium hypochlorite was used to assist ultrasonic regeneration respectively, the regeneration effect was enhanced to a certain extent. The addition of NaCIO was the most beneficial to ultrasonic regeneration among the three oxidants. With the increase of concentration of the oxidant, any of the three oxidants could make an increase in regeneration effect. But when the oxidant concentration was high to a certain extent, the regeneration efficiency decreased.Microwave was used to regenerate the adsorbent. It was found that microwave could regenerate the adsorbent well when the adsorbent was wet. When the adsorbent concentration was less than 5g/L, a smaller amount of water could help to achieve the best regeneration effect more quickly, but with the extension of microwave time, the regeneration effect decreased fast. At high adsorbent concentration 50g/L, better regeneration effect could be achieved more quickly when water was more. But the regeneration efficiency was lower than that at low adsorbent concentration. The lower the microwave power was, the shorter the time needed to achieve better regeneration effect was. The material and capacity of the container had some effect on microwave regeneration. The addition of hydrogen peroxide had no significant effect on microwave regeneration.When the adsorbent was first subjected to ultrasonic treatment and then irradiated by microwave, ultrasonic irradiation could significantly enhance the effect of microwave regeneration. Ultrasonic irradiation time had hardly any effect on regeneration. Water used to wet powder had great impact on regeneration. The regeneration effect decreased as the adsorbent concentration increased. But at adsorbent concentration less than 125g/L, the adsorbent could reach a good regeneration effect.The parameters of ultrasonic pretreated microwave method were optimized. Factors were listed contributing to regeneration efficiency as follow:powder amount, microwave time, water and microwave power. The optimum regeneration condition was powder amount of lg, microwave power of 600w, microwave time of 30min and water volume of 40mL. Under the condition and ultrasonic time of 5min and ultrasonic power of 120w, the regeneration efficiency was 100.14%. After 5 times regeneration, the regeneration efficiency was still higher than 98%.The physical and chemical characterization of fresh adsorbent and adsorbent regenerated by ultrasonic pretreated microwave process was carried out. Regeneration mechanism of this method was conjectured. The results showed that the adsorbent mainly comprised carbon nanotube, magnetic iron oxide and calcium carbonate; the magnetometer of adsorbent dropped from 15.25eum/g to 14.02 eum/g; the BET specific surface of adsorbent area increased from 131.15m/g to 145.89m/g; carbon element decreased slightly; but the shape, crystal form and surface functional groups of the adsorbent did not change significantly; ultrasound improved the dispersion state of the adsorbent in favor of subsequent microwave absorption. The magnetic iron oxide and carbon nanotubes could strongly adsorb microwave.Thus high temperature was achieved and the humic acid was heated to degradation while the adsorbent restored its adsorption sites and the adsorption function. |
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