Introduction
The conductivity of pulp water extract is a key parameter for evaluating the content of soluble ions in pulp, which can reflect the impact of chemical residues, washing efficiency and water quality during pulping. As an efficient and stable measurement tool, conductivity meters are widely used in quality control processes in papermaking, environmental protection, and chemical industries. This paper aims to systematically expound the method principle, operation steps and precautions for determining the conductivity of pulp water extracts using conductivity meters, and to provide technical reference for related testing work.
Principle of determination
Conductivity is a measure of the ability of a solution to conduct current, which is closely related to the concentration, mobility and temperature of ions in the solution. Inorganic salts (such as chloride, sulfate) and organic electrolytes in pulp water extracts are ionized under the action of electric fields to produce electrical conductivity. The conductivity meter calculates the conductivity according to the formula by measuring the conductivity value between the electrodes placed in the solution:
κ = G × K
where κ is the conductivity (unit: S/cm), G is the measured conductivity value (unit: S), and K is the electrode constant (unit: cm⁻¹). Measurements are temperature compensated, and results are usually corrected to a standard temperature (e.g., 25°C) to eliminate the effect of temperature on ion mobility rates.
Instruments and reagents
The required instruments include a conductivity meter (equipped with a temperature sensor and calibration function), electrodes (usually platinum-black or graphite electrodes), a thermostatic water bath, an analytical balance and glassware. The reagents are deionized water (conductivity less than 1 μS/cm) and standard potassium chloride solution (for electrode calibration). All utensils should be thoroughly rinsed with deionized water to avoid contamination.
Sample preparation
Weigh a certain mass (e.g., 2 g) of air-dried pulp sample, add deionized water (e.g., 100 mL), and extract in a constant water bath at a specified temperature (e.g., 95°C) for 1 hour. After cooling, it is filtered and the filtrate is collected as the water extract to be tested. If the filtrate is cloudy, it can be centrifuged to ensure measurement accuracy.
Assay steps
First, calibrate the conductivity meter: calibrate the electrode constant at the measured temperature with a standard potassium chloride solution. Then rinse the electrode with deionized water, immerse it in the filtrate to be tested, and record the conductivity value and solution temperature after the reading is stable. Each sample was measured three times in parallel and the average value was taken. After the measurement, clean the electrode in time and soak it in deionized water for storage.
Calculation and presentation of results
The measured conductivity value is converted into the conductivity at standard temperature by temperature compensation. The results can be expressed as the conductivity of the pulp water extract in mS/cm or μS/cm, and the conductivity value per unit mass of pulp is calculated for sample-to-sample comparison if necessary. The calculation formula is as follows:
κ25 = κt / [1 + α(t - 25)]
where κ25is the conductivity at 25°C, κtis the value measured at temperature t, and α is the temperature coefficient (usually 0.02/°C).
Influencing factors
The following factors need to be controlled during the measurement: electrode condition (contamination or aging can cause deviation), solution temperature (need to be accurately monitored and compensated), extraction conditions (time, temperature and water quality need to be consistent), and external interference (avoid electromagnetic fields or vibrations). It is recommended to periodically verify the electrode constant and use freshly prepared extracts to reduce ion sedimentation effects.
Application and Significance
This method is suitable for evaluating the washing effect of pulp, the purity of process water and the trend of ion accumulation in the production process. By monitoring changes in conductivity, the pulping process can be optimized, energy consumption can be reduced and product quality can be improved. Relevant standards such as ISO 6587 and GB/T 1545 provide methodological basis to ensure data comparability.
Summary
Conductivity meter to determine the conductivity of pulp water extract is an easy-to-operate analysis method with reliable results. Standardized operating procedures and strict quality control help obtain accurate data to support process improvement and environmental protection in the paper industry. In the future, automation technology can be combined to further improve inspection efficiency.
References
ISO 6587: Paper, board and pulps – Determination of conductivity of aqueous extracts.
GB/T 1545: Determination of conductivity of paper, cardboard and pulp water extracts.
TAPPI T252: Conductivity of pulp and paper water extracts.