Adsorption of the scale inhibitor, Diethylenetriaminepenta (methylenephosphonic) acid, DTPMP, on illite, kaolinite, Na-montmorillonite, and aluminum oxide was evaluated as a function of equilibrium concentration at constant temperature, pH and ionic strength. The experimental conditions used were typical of oil and gas formations, including a high ionic strength and moderate hardness. The work was done to quantify DTPMP adsorption on common subsurface materials, and compare DTPMP adsorption to ortho-phosphate, a well studied, strongly adsorbing oxyanion.
The experimental results showed that DTPMP adsorbed strongly to these surfaces, and suggested that adsorption was by ligand exchange. Adsorption on aluminum oxide and illite was especially high at low concentrations. This suggested bi-dentate adsorption at high energy surface sites and ternary adsorption on exchangeable polyvalent metals. The calculated DTPMP adsorption isotherms were consistent with isotherms describing ortho-phosphate adsorption, and successfully predicted adsorption curves on soils of known composition. Simulated 1-D column breakthrough curves, based upon DTPMP adsorption isotherms, varied from reported experimental curves. This was due to the non-equilibrium conditions which existed during the column studies.