Study On Scavenging Papermaking Anionic Trash By Hydrotalcites And Calcined Hydrotalcites

In this paper a potential applicability of hydrotalcites (HTs) and their calcined products (CHTs) as scavengers of anionic trash (AT) in papermaking whitewater was strdied by utilizing the special structures and characteristics of these compounds, in order to reduce the pollutants load in whitewater and reduced pollutants on the production and quality of paper adverse effects. The research results of this thesis not only have the positive role in promoting the cleaner production and energy-saving emission reduction in pulp and paper industry, but also have a certain reference value on the removal of pollutants in waste water from some other industries.The HTs with Mg/Al molar ratios of1:4,1:1,2:1,3:1and4:1(marked as HT-1/4, HT-1, HT-2, HT-3and HT-4, respectively) were prepared by co-precipitation method, and these products were calcined, and their calcined products (marked as CHT-1/4, CHT-1, CHT-2, CHT-3and CHT-4, respectively) were obtained. HTs prepared had the desired layered structure, and for the CHTs the layered structure was completely disappeared. Through SEM observation, the particle sizes of HTs and CHTs were estimated to be about5-50μm. The specific surface areas of the CHTs were greater than those of the HTs.The adsorptions of benzoic acid (BA) and p-toluenesulfonic acid (p-TSA) as lignin model compounds by the HTs and the CHTs at different pH values were firstly investigated. The equilibrium adsorption quantities significantly decreased with the increase of pH value. The kinetic data of the adsorption of BA by HT-2and CHT-2under an ambient temperature of293K could be fitted by pseudo-second-order equation. It was found that the adsorption isotherms obeyed the Freundlich equation. The adsorption of BA by HT was endothermic and the adsorption of BA by CHT was exothermic. The different adsorption mechanisms of BA by HT and CHT were revealed. The equilibrium adsorption quantities of p-TSA changed little with the increase of pH value. The adsorption isotherms obeyed the Langmuir equation. The maximum adsorption capacity was68.49mg/g at298K. The kinetic data of the adsorption of p-TSA by CHT-3could be fitted by intraparticle diffusion equation.The adsorptions of abietic acid (AA) by the CHTs from both aqueous colloidal suspension and aqueous solution were investigated, respectively. Removing AA from colloidal suspension using the CHTs showed that the removal percentage of AA at the pH value of6.8was larger than those at the pH values of7.8-9.8and the adsorption capacity was434.78mg/g at323K. the kinetic data were followed pseudo-second-order kinetic model and the adsorption followed the Langmuir isotherm. The adsorption process proceeded by physical adsorption. About80%of the equilibrium adsorption capacity of the original CHT was achieved after five use cycles. Removing the dissolved abietic acid (AA-) from aqueous solution using the HTs or the CHTs showed the adsorption amount of AA-increased with increasing the calcination temperature of HTs from300to500℃, but decreased with increasing the calcination temperature from500to600℃. The calcined products of the anion intercalated HTs possessed high adsorption ability for AA-except for sulfate anion. In contrast to the CHT adsorbed colloidal abietic acid (AA), the recycling ability of the CHT adsorbed AA-was poor, and only about20%of the adsorption amount of the original CHT was kept after5use cycles. The adsorption mechanism of AA-on the CHT, i.e., the partial structure reconstruction of the CHT, was proposed based on X-ray diffraction (XRD) analysis.The adsorption of anionic trash (AT) from model whitewater by the CHTs was investigated, and the results showed that the Mg/Al molar ratio of adsorbent has a little effect on the adsorption of dissolved substances (DS), colloidal substances (CS) and lignin. The adsorption percentages of CS, DS and lignin by CHT-3gradually increased with the increase of adsorption time. The adsorption percentages of CS, DS and lignin changed little with increasing pH of model whitewater. The adsorption percentage of DS increased with increasing adsorbent calcination temperature, and the adsorption percentages of CS and lignin increased with increasing adsorbent calcination temperature from300to500℃, but decreased with increasing calcination temperature from500to600℃. About92%of the adsorption percentage of the original CHT-3for CS and80%for lignin were achieved after five use cycles.