This research examined the hypothesis that lignin compounds form aqueous complexes with silica increasing its solubility, thereby inhibiting its precipitation. An experimental program using four lignin model compounds was conducted to test the hypothesis. Laser Raman spectroscopy (LRS) was used to characterize, qualitatively, the interaction between lignin and aqueous silica, and to identify the possibility of silica-lignin complexation. Solubility studies were then performed by analyzing the solubility of silica in presence and absence of lignin within the relevant pH range to confirm the results of LRS, and to obtain a quantitative assessment of the relative solubility. The findings have established the formation of silica-ferulic, silica-vanillic, and silica-4-methoxycinnamic acid complexes, but no evidence was detected for the formation of silica-veratryl alcohol complex. In fact, the black liquor undoubtedly contains much more complex lignin materials than the simple model compounds used in this work. The more complex lignin compounds are likely to have an even greater tendency to form silica complexes, thus contributing to the initial hypothesis. This finding provides a fundamental understanding as to why previous efforts to precipitate silica by lowering the pH from 10-11 (for black liquor) to less than 9 did not achieve satisfactory silica separation, and why alternative strategies need to be investigated.
Chitin, which is the second most abundant biopolymer next to cellulose, and can be extracted commercially from the shells of crustacean (such as crabs, shrimps, prawns, krill), insects, fungi, and yeast. It can be converted into chitosan by partially deacetylation process. chitosan, has unique and distinctive features like, biodegradability, nontoxicity, high reactivity, excellent chelation behavior due to the presence of amine and hydroxyl functional groups which show high adsorption potential for various aquatic pollutions, and low cost in comparison with other adsorbents. Chitosan was successfully produced in the laboratory from shell waste. The yield was about 42.34 gm dry chitosan with ratio of 15.3% from the dry shells. The produced chitosan has good solubility in 1% acetic acid solution, it achieved up to 96.3%. It has % D.D.A. with value of 63% to 80%. However, it has good performance in removal of metals from industrial wastewater, it is not recommended to use it in the raw form due to presence of undesirable characters; such as low mechanical strength, swelling, and solubility in acidic media. chitosan/Activated carbon composite overcome these undesirable features in chitosan and gave good performance in the remediation of wastewater.
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