Colloid-chemical phenomena in wastewater containing lignosulphonates

A.V. Sineva

Managing the wasterwater resource. Proceedings of the 4^th Intern.Conf. on Ecologocal Engineering for Wastewater Treatment. Eds. B.Klove at al. The Agricultural University of Norway, Aas, Norway. 1999, ch.11

ABSTRACT. The manuscript, which was represented at the Conference Ecoeng 99 for the poster section, reviews principal stages of water purification of wastewater containing lignosulphonates. The formation of disperse structures during the processes of water purification is an important condition of mineralization of technogenic substance as phenomenon which scientific bases were created by P.A.Rehbinder’s school. Taking the lignosulphonates of the different cationic form (Na⁺, Ca⁺², Al⁺³ or H⁺) and fraction (low molecular mass and colloid fractions) compositions, we considered some series of colloid-chemical phenomena, which are the basic adsorption methods of water purification of cycle wastewater at the factories of wood and paper industries. The series are as follow: adsorption on the different natural adsorbents (including internal adsorption); ion exchange; coagulation by chemical reagents; making the sediments waterless as well as the utilization of lignosulphonate for the purposes of agriculture.

The presence of man on the Earth is associated closely not only with the food production but also with the methods of reproduction of environment, the problems of creation of biotechnologies, free-of-waste technologies, the reasonable use of nature resources, the mineralization of technogenic substance, and etc. Each of the problems requires a certain consideration with the use of modern level of scientific knowledge and we think that it can be successfully solved by classical physical- or colloid-chemical methods. We devote special attention to the mineralization of technogenic substance / 1 /, when the mineralized substances, i.e., the products of living, wastes, and metabolites are involved again in continuos natural cycles of substance and energy exchange. The purification of water consists of extraction (removal) of admixtures present in cycle wastewater with the use of purification systems or conversion of admixtures into compounds, which do not pollute soil, water, and air; thus, the water purification is a part of the mineralization process. From this point of view, let us present briefly the literature and our data on the studies of colloid-chemical phenomena in wastewater of cellulose-paper industry and consider the ways of controlling the wastes.

The wastewater of cellulose-paper industry contains mainly biologically non-degradable derivatives of lignin in the form of lignosulphonates (LS) or lignin sulphate (thio-lignin) or lignin produced by hydrolysis. In our work we investigated LS water solutions of different cationic nature by means of gel-filtration on the sefadeks following the spectrophotometrical detection and quantitative treatment of eluent curves / 2, 3 /. The fact that the water solutions of LS are bifractional was supported and the dependence of fraction composition on the cationic composition was found for the studied LS of sodium, calcium, and aluminium. The observed redistribution of the components in the mixtures of low molecular mass fractions (LF) and colloid fractions (CF) is considered in terms of inner adsorption, namely, the adsorption of molecules of truly soluble LF on the particles of CF (Goring's microgel / 4 /). The calculation was made for the adsorption of truly soluble LS on the CF of studied forms. Besides, non-ion exchange character of internal adsorption was shown in the mixtures of LS / 5 /. The peculiarities observed for LS in water solutions determine the character of adsorption of LS on the formed or newly forming solids that is the base of adsorption purification of wastewater. For example, the LS is fractionated on the purification systems depending on the nature of solid adsorbents (fresh cement, gypsum free clinkers, and calcium and magnesium oxides during their hydration / 2 / as well as natural minerals, grounds, and soils) in such a way that either CF or LF is adsorbed. Varying the solid-water ratio and the concentration of LS, the separation can be carried out to a different extent even to absolute extraction of the required fraction.

The process of physical-chemical purification of wastewater usually carried out by the coagulation when the salts of multivalent ions, e.g., Al⁺³ that neutralize the surface charge of colloid particles of LS are added. It is necessary to note the anomalies in adsorption when юl-form appears as the result of ion exchange. Hydrolysis of the Al-form of LS can result in the formation of hydroxyl complexes between Al⁺³ and basic salt and also positively charged products of polycondensation, which block their exchange centers and decrease the internal adsorption while interacting with the negatively charged LS molecules. These products can also escape to a separate phase of the colloid dispersion. The interactions of the soluble (oligomeric) LS portion with exchange centers of the Goring’s microgel and the surface of the dispersed hydroxide particles probably by an anion exchange mechanism should be also considered. However, we can not totally exclude the possible formation of surface LS chelates with Al³⁺. Thus, the fractionation of LS requires that the role of each of the mechanisms be established in the determination of the sorption capacity of the colloid systems under investigation / 5 /. Taking into account the toxicity of the Al salts, one can consider the given anomalies as the base for replacement of the known coagulant Al₂(SO₄)₃, e.g., bentonite clay. The processes occurred when the sediments are made waterless under the conditions of movable filtration as well as the phenomenon of sineresis studied slightly for watered sediments of LS are also associated with the unreversible coagulation. The transformation of technogenic substance into biologically inactive state and its return into lithosphere occur namely via such structured sediments.

The problem of utilization of treated sediments of LS concerns with the searching for and explaining the possibilities of their application in particularly in agriculture.

1. O.I.Lukyanova and O.G.Novozhilova,
   Physical-chemical mechanics of natural disperse systems, Moscow: MSU, 1985, p. 241.

2. O.I.Lukyanova, N.F.Pilinskaya and E.S.Solov'eva,
   Kolloidn. Zhur. 1979, v. 41, p. 684.

3. N.I.Niklyaeva, O.I.Lukyanova, and A.V.Sineva,
   Kolloidn. Zhur. 1983, v. 45, p. 451.

4. A.Rezanovich and D.A.J.Goring,
   J.Colloid Sci. 1960, v. 15, p. 452.

5. A.V.Sineva,
   Colloid Journal, 1991, v. 53, p. 740.

Laboratory of Physical and Chemical Mechanics