(381aj) Effect of Organic Matters on the Fractional Crystallization Process of High-Saline Wastewater from Coal Chemical Industry

Effect of organic
matters on the fractional crystallization process of high-saline wastewater
from coal chemical industry

Chao Bian^†, Hang
Chen^†¡ì, Xingfu
Song^*†‡¡ì, Jianguo Yu^†

^† State Environmental Protection Key Laboratory of Environmental
Risk Assessment and Control on Chemical Process and ^‡ National
Engineering Laboratory for Industrial Wastewater Treatment, East China
University of Science and Technology, Shanghai 200237, China

^¡ì Shanghai Institute of Pollution Control and Ecological Security,
Shanghai 200092, China

*Corresponding author: xfsong@ecust.edu.cn

Abstract

High-saline wastewater from coal chemical industry contains a large amount of inorganic
salts and complex organic matters. The direct emission can cause the pollution of environment and the waste of resources. As a result, the
treatment of high-saline wastewater from coal chemical industry has become an
urgent problem to be solved in China. The zero discharge technological
requirement with the core concept of fractional crystallization attracted wide attentions, which not only concerns on the water
treatment but also focuses more on the recycle of the dissolved inorganics.

The typical inorganic system is Na⁺//Cl^-,
SO₄^2-, NO₃^--H₂O. Till
now, a series of researches on the thermodynamics of the quaternary system and
its subsystems have been reported^1-5. Based on the abundant thermodynamic data, the
fractional crystallization process was designed and optimized. As shown in Figure 1, Na₂SO₄, NaCl and NaNO₃ can be successively recycled from the system Na⁺//Cl^-, SO₄^2-, NO₃^--H₂O by the integration of pretreatment, membrane concentration and
fractional crystallization.

Figure 1. The schematic diagram of the treatment
process

A kind of
practical high-saline wastewater of coal chemical plant was treated according
to the route. The analysis results indicate that the purity of all products
meet the index of industrial salt. And the corresponding SEM pictures were
established in Figure 2. However, the concentration of COD in the products is
about 300 mg/L, which has certain restrictions on the subsequent application of
the products. Moreover, the organic matters
in the wastewater were continuously enriched during the crystallization
process, which may affect the fractional crystallization process, thereby
influencing the morphology and quality of the products. Therefore, it is
necessary to investigate the effect of organic matters on the crystallization
process and clarify the influencing mechanism between organic matters and inorganic
salts.

Figure 2. The SEM pictures of production (a-Na₂SO₄,
b-NaCl, c-NaNO₃)

Morphological prediction of the pure crystals
was realized by AE model using Materials Studio, as
shown in Figure 3. The influencing mechanism of some different types of organic
matters on the products will be studied further through the combination of
experiment and simulation. The research results will provide a theoretical
basis for improving the product quality and optimizing the flowsheet.

(a)                             (b)                    
(c)

Figure 3. Morphological prediction of the crystals by AE
model (a-Na₂SO₄, b-NaCl, c-NaNO₃)

Keywords: high-saline
wastewater, fractional crystallization, organic matters, influencing mechanism,
morphological prediction

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