Study On The Adsorption Performance Of Lignosulfonates On Surface Of Solid Particle

Lignosulfonates(LS) is an abundant, low price and renewable polymer, which is a by-product from pulp and paper process. With a complex, macromolecular structure carring negatively charged sulfonate, hydroxyl, phenolic, and carboxyl groups, LS is an anionic polymer inwhich the essentially hydrophobic backbone is rendered hydrophilic by substitution of sulfonate groups.One of the most important applications of LS is used as dispersants, which can prevent the clumping and settling of undissolved particles in suspensions. By attaching to the particle surface, it keeps the particle from being attracting to others.LS and its modified products used as dispersant has been widely studied. However, LS is a natural polymer. Its characters, wide distribution of molecular weight, complex, multi-group elements and so on, bring great difficulties to reveal the mechanism of its adsorption behavior on the solid surface. The surface activity of LS lets it adsorb on the surface of solid surface, which endow the particle surface excellent hydrophilicity and electro negativity. So the dispersion of solid particles in aqueous solution is associated closely with the adsorption of LS on solid surface. The adsorption characteristics of LS on solids are influenced by the charge property of solid surface, the hydrophilic group, molecular weight, etc.However, it is difficult to explore the adsorption mechanism of LS due to the adsorbent's complex composition and diverse morphology. To minimize effect of impurities, morphology and other factors, we selected TiO₂ and activated carbon as adsorbent. Adsorption kinetics and thermodynamics were studied in this dissertation. Adsorption forces between sodium lignosulfonate(SL) and the TiO₂ particles or activated carbon were investigated by the influence of pH, urea and salts. By means of the GPC, FTIR, UV, XPS, AFM and other analytical methods the adsorption mechanism was revealed.The results show that the adsorption kinetics of SL on the surface of TiO₂ particles meets the Langmuir adsorption rate equation. Adsorption activation energy is equal to 7.826 kJ·mol^-1. Thermodynamics results show that increasing temperature is beneficial to adsorption process and the thermodynamic parameters is obtained as follows,ΔH _ad=2.373 kJ·mol^-1,ΔS _ad=0.11 J·mol^-1·K^-1,ΔG _ad^Θ=-30.6 kJ·mol^-1(30℃). Mainly through the weak adsorption of hydrocarbon chains and particle surface of the hydrogen bond, electrostatic interaction, hydrophobic effect and other physical and chemical adsorption SL adsorbed on the TiO₂ particle surface. Zeta potential test results show that isoelectric point of TiO₂ particles is 4.17 and SL is negative electrification in aqueous solution. After absorbing SL, TiO₂ particles's electronegativity has been enhanced. When the equilibrium concentration of SL is 0.83 g·L^-1, Zeta potential of TiO₂ particles decreases from -34.9 mV to -57.46 mV. GPC results indicate that the high molecular weight SL first adsorbs on the TiO₂ surface. With the increase of pH value, absorption amount and rate of SL reduce. With the addition of salt, absorption amount and adsorption rate increase significantly. After adding salt, adsorption processs is conducted in accordance with Freundlich equation. In particular, CaCl₂ made saturated adsorption amount of SL increases from the 4.7 mg·g^-1 increased to 12.0 mg·g^-1. XPS results show that salts made the adsorption layer get thicker, where cation adsorbed with SL on the TiO₂ surface but anion did not. In particular, CaCl₂ made adsorption layer thickness of SL increased from the 4.9 nm to 11.8 nm. The analysis of the AFM on the fracture surfaces of adsorbed SL quartz showed that the cation increases the adsorption amount by making the SL gather into cluster, while anion increases it by making SL molecule smaller, increase monolayer adsorption density. Urea let the adsorption amount of SL decrease 11%, because it can damage the hydrogen bonding. So hydrogen bonding plays a major role in adsorption process. XPS results show that urea can form hydrogen bonds with SL adsorbing on TiO₂ particles. FTIR also shows that the surface of SL and TiO₂ particles exist a strong hydrogen bond.Adsorption kinetics showed that the process of SL adsorbing on activated carbon meet the Langmuir adsorption rate equation. Thermodynamic results show that the adsorption process little affectes by temperature. Through the weak adsorption of hydrocarbon chains and electrostatic interaction and drilling into pore, SL adsorbes on activated carbon. Zeta potential results indicate that the isoelectric point of activated carbon was 3.79. After adsorbing SL, activated carbon's electronegativity has been enhanced. Its Zeta potential of activated carbon decreased from -36.7 mV to -44.2 mV. GPC results show that the low molecular weight SL first adsorbs on activated carbon. With the increase of pH value, absorption amount and adsorption rate reduce. With the addition of salt, adsorption amount of SL and the adsorption rate increase significantly. Adsorption process of SL on activated carbon accords with Freundlich equation when the salts exist. Urea reduces the degree of aggregation of SL and made adsorption amount reduce by 26%. In the presence of urea, the adsorption process is not only consistent with Langmuir equation, but also Freundlich equation. XPS results show that urea may be through hydrogen bonds connecting with SL and adsorbed on activated carbon surface. Straight chain alcohols of C₄, C₈, C₁₀ make the adsorption amount significantly increases, where adsorption amount increases from 35.2 mg·g ^-1 to 83.4 mg·g ^-1. This study selected the polarity, hydrophilic TiO₂ and non-polar, hydrophobic, porous activated carbon as adsorbent to study the adsorption properties of SL on their surface. The results show that the adsorption of SL enhances electronegativity. Increasing of pH makes the adsorption amount of SL reduce. In the presence of salts, the adsorption amount of SL increases. Adding urea let the adsorption amount decrease. For TiO₂, the adsorption capacity and adsorption rate increase with increasing temperature and high molecular weight SL will first adsorb on the TiO₂ surface; while for activated carbon, the temperature has little effect on the adsorption capacity and adsorption rate and low molecular weight SL will first on activated carbon surface. In this dissertation, adsorption mechanism is initially revealed. This study can provide experimental data and theoretical basis for the research on adsorption of SL on these two types of solid particles.