Investigation of Thiosulfate Adsorption on 316 Stainless Steel in Neutral Solutions by Radioactive Labeling, Electrochemistry, and Auger

We report on thiosulfate adsorption on a 316 stainless teel electrode in neutral solutions by radiochemical, electro-chemical, and Auger electron spectroscopy (AES) measurements. In contrast to previous work on thin metal films or metal electrodeposits to model real-life metal (alloy) samples, our radiochemical approach permits coverage measurements of labeled adsorbates on smooth solid electrodes of convenient size and thickness. A dedicated electrode preparation yields a reproducible surface for fast and reversible thiosulfate adsorption from a perchlorate solution. However, on the same time scale, reversible adsorption is impeded in sulfate media. Further, no thiosulfate adsorption occurs in borate buffer solution, and complex thiosulfate adsorption behavior predominates in solutions containing varying amounts of chloride anions, initially increasing with bulk chloride concentration, maximal at 10-4 to 10-SM CI-, and decreasing at higher chloride concentration. We conclude that small amounts of surface chloride assist he thiosulfate adsorption, but increasing surface C1- coverage becomes competitive to that of thiosulfate. The chloride adsorption enhancing mechanism probably results from a destabilization f the locally ordered thiosulfate surface structure. Radioehemistry and AES show that long expo-sure to thiosulfate solutions results in permanent thiosulfate immobilization on the stainless teel surface