Influence of PPCA (phosphinopolycarboxylic acid) and DETPMP (diethylenetriaminepentamethylenephosphonic acid) on silica fouling

Silica is perhaps the most undesirable inorganic deposit formed in processing industrial waters and it presents a challenge for desalination systems used for brackish or seawater desalting. It may form hard and tenacious deposits that are difficult to remove. This paper is focused on silica formation, deposition and its inhibition in desalination applications by following the kinetic of silica formation and morphometric characteristics of deposits. Kinetic of precipitation was studied in supersaturated silica feed solutions close to real conditions. Jointly, the morphological characteristics of precipitate such as size or shape factor were studied in the micrometric range by image analysis. The inhibition performance of chemical inhibitors [phospinopolycarboxylic acid (PPCA) and diethylenetriaminepentamethylenephosphonic acid (DETPMP) were investigated. Experimental results show high effects on the inhibition efficiency of these molecules as soon as their concentrations reach 50 ppm. The deposition of silica was highly delayed and the morphological characteristics of the deposit such as size were affected by the presence of inhibitors. Moreover, in this paper, the role of pH in silica formation and inhibition in waters relevant to desalination systems is discussed.