A study on the impact of NH3/NH4+ buffer solutions on chlorides and iron salts from archaeological iron, utilizing pH measurements: introduction of a new dechlorination method and a testing procedure

This paper examines the use of NH 3 /NH 4 + buffer solutions for the dechlorination and desalination of archaeological iron objects. The research leverages the chemical affinity of ammonia for chlorine ions or other functional chemical groups, which can form ammonium salts. The study evaluates the effect of NH 3 /NH 4 + buffer solutions on NaCl, KCl, FeCl 3 , Mohr salt, synthetic akaganeite, seawater, and other substances through pH-metry measurements. Added chlorides mimic those found in extracted samples like archaeological iron. During dechlorination, ammonium chloride forms, as shown by NH 4 + ions, which immediately affect the pH of the NH 3 /NH 4 + buffer. This method, using Serial mode data acquisition and Matlab graphical methods, like Plots and Linear Regression, identifies ongoing dechlorination and establishes the conditions for its completion. The slope of the regression curve—regardless of whether it is linear, cubic, or another form—serves as an indicator for the current stage of the dechlorination reaction. A negative slope signifies that dechlorination is ongoing, while a transition from a negative to a horizontal (zero) slope denotes completion of the dechlorination or desalination process. Conversely, a positive slope in the regression curve appears exclusively in solutions undergoing buffer regeneration.