Refractive Index of Black and Green Liquors

Abstract

Lack of reliable data on the optical properties of black and green liquors complicates control of their composition in technological process of sulphate cellulose production. In this regard the paper presents measurement results of refraction index of black liquors n (k,t) at concentration in solutions of bone-dry solids up to k = 70% and at temperatures t = 10-90 °C, as well as in green liquors n(C,t) at the total alkalinity of C = 0-250 g/l and in the same temperature range. All samples of solutions of black and green liquors were provided by Segezha Pulp and Paper Mill and certified in factory laboratory. Measurements were taken by means of the laboratory Abbe refractometer (URL-1), digital refractometer "Expert pro", goniometer spectrometer GS-5, and ultra-violet spectrophotometer as well. The work also presents optical D density spectra in the ultra-violet region of the wavelengths for the samples of a green liquor and main mineral component to form it, i.e. Na2S (sodium sulphide). To calculate dispersion of n (λ) in the visible spectral range, here a Lorentz single-oscillator model was used. The paper discusses study results of dispersive dependence of refraction index in green liquors with various concentration and chemical components of n (λ, C) forming them at t = 20°C. Computing and experimental dependences of n (λ) had not only good qualitative, but also quite satisfactory quantitative compliance. The work also describes main mineral components defining optical properties in these liquors. Given here data on concentration and temperature dependences of a refraction index in black n(k,t) and green n(C,t) liquors have been never published before. These data are of essential interest to control soda recovery technologies in manufacturing sulphate cellulose. The received results can be also used to tune and calibrate modern domestic and foreign industrial refractometers.

Keywords

• refractive index
• thermooptic constant
• black and green liquors