Rapid Determination of Total Dissolved Solids in Black Liquors by ATR-UV/VIS Spectroscopy, 2004 International Chemical Recovery Conference

This work reported an attenuated total reflection (ATR) UV/Vis spectroscopic technique for rapid determination of total dissolved solids (TDS) content in both weak and concentrated black liquors. It was based on measuring the dissolved lignin absorption in black liquor at a wavelength of 280 nm or higher using a spectroscopic technique. Since the amount of other non-absorbing species, such as inorganic salts and dissolved carbohydrates, in the black liquor can also affect the refractive index of the solution, the effective optical path length in the ATR measurement was subject to change. Thus, the ATR absorption intensity for dissolved lignin measurement also includes information about the other dissolved solids in the liquor. Results showed that the square-root of the ATR signal is linear to the TDS content in the corresponding weak black liquors over the range of 7-23 %. For the concentrated black liquors (TDS from 58 to 72 %), the relationship between ATR response and TDS content can be regarded as linear. This ATR technique is simple and can be easily implemented in a process line for on-line liquor TDS monitoring.