Evaluation of Environmentally Benign New Chemical Rust Removing Agent- Hydroxy Ethane Diphosphonic Acid (HEDPA)
NAVAL SURFACE WARFARE CENTER CARDEROCK DIV BETHESDA MD
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In order to evaluate the adaptability of hydroxyethane diphosphonic acid HEDPA as an environmentally benign alternative rust removal agent, the present investigation was undertaken. The effectiveness of HEDPA was studied as a function of acid concentration in the range 2-20 vol. and at different temperatures in the temperature range 23 deg C-55 deg C. The results suggest that the acid HEDPA is very effective to remove the rust and the rate of rust removal depends upon the acid concentration andor the solution temperature. Once an optimum value is reached, further increase in either the acid concentration andor the solution temperature has a negative effect on the rust dissolution kinetics. In addition, it was also found that the chemical treatment with concentrated HEDPA solution concentration range 5-20 vol. HEDPA produces rust free steel samples with very rough surface topography. The chemical processing at higher temperatures 40 deg C-55 deg C, and higher HEDPA concentrations 5 vol. , produces strong pungent smell and an unpleasant cleaning environment. The most effective HEDPA concentration and temperature for the rust removal appears to be 2-4 vol. and 40 deg C respectively. The activation energy for the rust dissolution process using 2-4 vol. HEDPA was in the range 12 2 kcalmole. The activation energies for rust dissolution by 5, 10 and 20 vol. HEDPA were found to be 20, 28 and 32 2 kcalmole respectively. The reaction product contains a mixture of various higher order iron phosphates. The soils that were contaminated low concentration 0.5 wt. of with the reaction products improved the germination of seeds and the plants that were fed with solution containing the chemical reaction by products up to 0.5 wt. were healthy and increased in their size. Above 0.5 wt. , the trends were reversed.
- Physical Chemistry
- Properties of Metals and Alloys