DEASHING OF SULFITE-ALCOHOL STILLAGE CONCENTRATES

V. M. Vityugin, E. S. Plotnikova

(Presented by the scientific seminar of the Department of Mineral Processing)

Concentrates of sulfite-alcohol stillage (SAS), which are evaporated residues after fermentation of sulfite liquor, are surface-active substances capable of being adsorbed on the surfaces of various bodies. The diverse properties of SAS concentrates make it possible to use them as foundry binders, emulsifiers, dispersants, plasticizers, adhesives, etc. In addition, sulfite-alcohol stillage is a generally recognized binding additive in the granulation and briquetting of fine materials.

Sulfite-alcohol stillage concentrates, as binding materials, possess excellent adhesive properties with respect to materials of both organic and inorganic origin. They mix well with any additives, readily dissolve in water at any concentration, require no special preparation, are inexpensive, are not in short supply, are harmless to service personnel, etc.

But some branches of industry impose increased requirements on sulfite-alcohol stillage with respect to the content of mineral impurities.

The SAS concentrates currently in use usually have an ash content of 12–17%, which is due to the content in them of calcium salts of lignosulfonic acid.

In recent years, extensive studies have been carried out aimed at improving the technological properties of sulfite-alcohol stillage (1, 2). These studies have established that the binding ability of SAS is substantially improved when the calcium ion is replaced by monovalent ions of potassium, sodium, and especially ammonium.

As a result of the cation-exchange reaction (1), the corresponding salt of lignosulfonic acid and an insoluble calcium salt, which precipitates, are formed in solution:

\[ (\mathrm{R—SO_3})\mathrm{Ca} + (\mathrm{NH_4})_2\mathrm{SO_4} \to 2\mathrm{RSO_3NH_4} + \mathrm{CaSO_4}. \]

Treatment of sulfite-stillage concentrates with ammonium carbonate and ammonium sulfate makes it possible to remove calcium salts and thereby leads to a reduction in the content of mineral impurities in SAS.

To determine the conditions of the process for deashing concentrates of sulfite-alcohol stillage, an experimental study was carried out.

Deashing of SAS concentrates was carried out on foundry concentrates of grade KTB, obtained from the Solikamsk Pulp and Paper Combine. The quality of the concentrates met the requirements of GOST 8518-57. Preparation of the initial SAS concentrate consisted in dissolving it to a specified specific gravity in water at 40–50°C. Table 1 gives analytical data for the initial solution of sulfite-alcohol stillage.

Table 1

In selecting reagents for precipitating calcium salts in sulfite-alcohol stillage in order to reduce its ash content, the following factors were taken into account:

1) the degree of contamination of SAS concentrates by harmful impurities during precipitation;

2) the form of the chemical compounds in which the ash components occur;

3) the possibility of regenerating the precipitant.

An approximate calculation of the required amount of precipitant was made according to equation (1), based on the calcium oxide content in the initial sample. Precipitation was carried out at a temperature of 18°C. The precipitate was allowed to settle for a certain time, then filtered on a vacuum funnel. The filtrate was evaporated on a water bath, dried at a temperature of 100–105°, and analyzed for ash.

The first series of experiments was intended to determine the effect of the type of precipitant and its amount on the ash content of the filtrate and the completeness of precipitation.

The following reagents were selected for the study: \((\mathrm{NH}_4)_2\mathrm{CO}_3\), \((\mathrm{NH}_4)_2\mathrm{SO}_4\), \(\mathrm{H}_2\mathrm{SO}_4\). All reagents were used in the form of saturated solutions. Experiments were carried out with different amounts of precipitants, determined as a percentage of the theoretical amount. The theoretical amount of reagent was taken to be that amount at which precipitation practically ceased and the ash content of the filtrate stopped changing. The theoretical amount of precipitating reagent was established in experiments using \((\mathrm{NH}_4)_2\mathrm{CO}_3\).

As can be seen from the experimental results, ammonium carbonate deserves the greatest attention, giving an ash content of about 1% with an amount of precipitant close to the theoretical value. Ammonium sulfate, although it is a cheaper and less scarce reagent, gives, at the same amounts, a smaller reduction in ash content than ammonium carbonate.

Table 2

In the next series of experiments, the effect of the precipitation reaction time was studied at a constant amount of precipitant, $(\mathrm{NH}_4)_2\mathrm{CO}_3$, equal to 62.5. The precipitation times were 1, 3, 6, 9, 24, and 13.5 hours. The experimental results are given in Table 3.

Table 3

It is evident from Table 3 that the precipitation reaction lasts for 9–10 h. After this time, precipitation practically ceases and the ash content of the filtrate remains constant.

Next, an attempt was made to cheapen and simplify the deashing process of SSC by replacing ammonium carbonate with carbon dioxide gas and ammonia water. This gave positive results: when 2.93 l of $\mathrm{CO}_2$ was passed through 100 ml of an SSC solution of specific gravity 1.17 with 20.4 ml of $\mathrm{NH}_4\mathrm{OH}$ (25% solution) added to it, the ash content of the filtrate decreased to 0.83%; approximately the same result was obtained when 4 l of $\mathrm{CO}_2$ was passed through the solution. A more detailed study of the process of deashing sulfite-alcohol stillage with the aid of ammonia water and carbon dioxide gas will evidently make it possible to develop an inexpensive and simple technology.

Conclusions

1. In treating SSB concentrates with various precipitants, the best deashing results are obtained by using ammonium carbonate.

2. When sulfite-alcohol stillage is treated with ammonium carbonate, its ash content decreases in proportion to the amount of precipitant.

3. As the duration of the precipitation reaction increases, the completeness of precipitation increases and the quality of the deashed filtrate improves. After 9–10 hours, the time factor ceases to exert its influence.

4. The use, as a precipitant, of ammonia water and carbon dioxide instead of ammonium carbonate reduces the cost of the process, simplifies the technology, and improves the results of deashing. Further, more detailed investigations are being carried out in this direction.

References

1. A. V. Buevskoi, S. A. Sapotnitskii. Proceedings of the S. M. Kirov LTA, 1950.

2. Handbook of core binder materials in foundry production. 1950.