Molecular Dynamics Simulation Of The Adsorption Of Polymers On The Surface Of Calcium Silicate

In the soda-lime sintering process of alumina production, calcium silicate dissolves easily in the leaching process, resulting in the dissolved alumina entered the red mud again, which is called the secondary reaction. If sodium polyacrylate (PAA) or polyethylene glycol (PEG) is added in the leaching process, it can inhibit the secondary reaction by adsorbing on the surface of calcium silicate, which improves the leaching rate of alumina.In the leaching process, polymer has a low concentration. Adsorption on the calcium silicate surface occurs only in a small area. So it is difficult to conduct experiments, calculation, and analysis on this process. But these difficulties can be overcome by the molecular dynamics simulation. It can simulate the process of absorption in the atomic or molecular scale, and plays an important role in the connection of macro characteristics and microstructures. Therefore, the computer simulation is an effective method to reveal the relationship of phenomenon and principle. And it is considered to be the third way of scientific research apart from theoretical analysis and the macroscopic experiment.In this paper, according to the adsorption theories on polymer and crystal surface, these results are achieved:foundation of all-atom simulation model of polymer PAA, PEG and calcium silicate, simulation on the process of polymer molecules adsorbing on the surface of calcium silicate; the adsorption energy of solid-liquid interface; the radial distribution function of the polymer on the surface of calcium silicate; the effect of these factors such as polymer structure, different calcium silicate crystal orb, different temperature and polymer chain link numbers to the adsorption energy; the micro component and explanation of the macro-kinetics and macro dynamic.The main results are as follows:Adsorption energy between polymer and calcium silicate changes in different crystal faces, it also varies in vacuum. Adsorption energy reaches the maximum, namely the strongest absorption power on face (110) between different crystal faces of β-C2S and PAA or PEG. It can be ordered as follows (from strong to weak):(110)>(010)>(011)>(001)≈(101)>(100), and the energy of PAA is stronger than PEG. In solution, the maximum of adsorption energy between PAA and calcium silicate is in face (011), while it is face (010) between PEG and calcium silicate. In conclusion, the adsorption energy is stronger in vacuum than in solution because the small molecule has a bad effect on the adsorption of polymer and calcium silicate.Between343.15K and363.15K, temperature has little impact on the adsorption. In low degree of polymerization, the longer of the polymer chains, the more chain link become sensitive of adsorption, so the adsorption energy is stronger. The simulated results were consistent with the experimental results. In the same condition, the polymer PAA and PEG has different adsorption energy on the surface of calcium silicate. And the adsorption of PAA with carboxyl is better than PEG with oxygen atoms.The radial distribution function draws from the environment simulation show that the water molecules adsorbed on calcium silicate crystal surface is multi-layer absorption. Hydrogen bonds are the main energy between polymer and water molecules. Sodium ion adsorbs oxygen atoms more easily than hydrogen atoms in water molecules.