Adsorption of lead in fixed-bed column using sodium carbonate treated rice husk

• Main Author: Chea, Sovattei
• Format: text
• Language: English
• Published: Animo Repository 2013
• Subjects: Sewage—Purification—Adsorption; Rice hulls; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/4435; https://animorepository.dlsu.edu.ph/cgi/viewcontent.cgi?article=11273&context=etd_masteral
• Institution: De La Salle University

Lead is a harmful and toxic heavy metal when found in water from the discharge of industrial wastewater. Lead concentrations in water are increasing progressively in the Philippines. It is extremely toxic to human health and the environment. Lead toxicity can cause a number of diseases and also can lead to death when present in the human body at higher concentrations than the permissible limit. To curtail this problem, adsorption by agricultural waste and by-products has been reported to be an acceptable method for heavy metal removal among the other technologies. The untreated rice husk (URH), an agricultural waste and by-product, abundant in the Philippines and available at low cost, was used in this study as an adsorbent as well as sodium carbonate treated rice husk (SCT-RH) and tartaric acid treated rice husk (TAT-RH) for lead removal from synthetic wastewater in a fixed bed column. The characterization of rice husk before and after treatment was conducted using BET, BJH, SEM, FTIR and pHPZC. The results showed that URH is a porous adsorbent which has a surface area of 4.384m2/g, while the TAT-RH and SCT-RH were found to have a smaller surface area of 1.364m2/g and 1.995m2/g, respectively. The results of pore size distribution showed SCT-RH is the best among the three adsorbents which consists of mesopore and macropore. SEM imaging showed that the surface of the adsorbents was changed before and after the treatment. The OH functional group was found to be present in the three adsorbents which are important in binding with lead ions. The pHPZC has been found to be 6.9, 1.95 and 8 for URH, TAT-RH and SCT-RH, respectively. Therefore, the pH of solution should be higher than 7 for URH and SCTRH, however, pH of >7 caused the precipitation of lead ions. In this study, the effect of adsorbent bed height, flow rate and initial lead concentration was investigated for lead removal in fixed-bed column. The results show that an increase in adsorbent bed height from 3 to 9cm increased the bed adsorption capacity from 0.818 to 1.946mg/g, 0.273 to 1.727mg/g and 2.946 to 4.091mg/g for URH, TAT-RH and SCT-RH, respectively. The increase of flow rate from 5 to 15mL/min resulted in the decrease in the bed adsorption capacity from 1.946 to 0.982mg/g, 1.727 to 0.409 and 4.091 to 2.127mg/g for URH, TAT-RH and SCT-RH, respectively. An increase in initial lead concentration of 10 to 190mg/L increases the bed adsorption capacity from 1.946 to 3.006mg/g and 4.091 to 8.809mg/g for URH and SCT-RH, respectively. SCT-RH was found to have the highest breakthrough time 22.5 hours and effluent volume 6.75L. The Bed Depth Service Time (BDST) Model was used to predict the operating parameter on the effect of adsorbent bed height. The results revealed that BSDT fitted well with the experimental data which gave R20.98. The minimum adsorption bed height was predicted to be 2.17, 2.56 and 1.33cm for URH, TAT-RH and SCT-RH, respectively. The Thomas Model also described well the adsorption capacity and the predicted breakthrough curves on the effect of flow rate and initial lead concentration of the three adsorbents, especially at low flow rate and low initial lead concentration. In conclusion, rice husk can be considered as a good adsorbent for the removal of lead from wastewater. Treatment of rice husk with sodium carbonate was found to be better than tartaric acid treated rice husk. The adsorption capacity of the three adsorbents follow the order of TAT-RH