Molecular Dynamics Simulation of Interaction between Calcite Crystal and Phosphonic Acid Molecules

The interactions between calcite crystal and seven kinds of phosphonic acids, nitrilotris(methylphosphonic acid) (NTMP), nitrilo-methyl-bis(methylphosphonic acid) (NMBMP), N,N-glycine-bis(methylphosphonic acid) (GBMP), 1- hydroxy-1,1-ethylenebis(phosphonic acid) (HEBP), 1-amino-1,1-ethylenebis(phosphonic acid) (AEBP), 1,2-ethylenediamine-N,N,N′,N′-tetrakis(methylphosphonic acid) (EDATMP), and 1,6-hexylenediamine-N,N,N′,N′-tetrakis- (methylphosphonic acid) (HDATMP) have been simulated by a molecular dynamics method. The results showed that the binding energy of each scale inhibitor with the (1l̄0) (1l̄0) face of calcite crystal was higher than that with (104) face, which has been approved by the analysis of pair correlation functions. The sequence of scale inhibition efficiencies for phosphonic acids against calcite scale is as follows: EDATMP>HDATMP>HEBP>NTMP>GBMP>HEBP>NMBMP, and the growth inhibition on the (1l̄0) face of calcite was at the leading status. Phosphonic acids deformed during the binding process, and electrovalent bonds formed between the phosphoryl oxygen atoms in phosphonic acids and the calcium ions on calcite crystal.