Influence and mechanism of alkali-modified sludge on coal water slurry properties

Municipal sludge (MS) is used to prepare coal water slurry (CWS). This practice is beneficial for resource utilization and reduces treatment costs and environmental pollution. In this study, alkali-modified municipal sludge (AMS) was prepared with Ca(OH)₂ as modifier and mixed with coal to produce AMS-CWS. The effect and mechanism of MS and AMS on slurry ability, stability, and combustion characteristics of the CWS were explored. The results of the pulping experiments showed that the slurry concentration of the AMS-CWS was approximately 10% greater than that of MS-CWS. The water separation rates of MS-CWS and AMS-CWS were 5% and 5.26%, respectively, which were 13.62% and 13.36% less than that of CWS (18.62%). The zeta potential experiments verified these results. Combustion performance research shows that both MS and AMS have positive effects on combustion performance. The results of the contact angle experiments showed that the hydrophobicity of AMS was enhanced, which was beneficial for improving the pulping capacity of MS-CWS.

The effect of inorganic salt in wastewater on the viscosity of coal water slurry

The preparation of coal water slurry (CWS) using wastewater, which contains inorganic and organic components, is one method of wastewater utilization. In this study, the effect of inorganic salts on the viscosity of CWS was examined. The results show that monovalent salts (NaCl, KCl) decreased the viscosity of CWS. The viscosity of CWS was not affected by bivalent salts (CaCl₂, MgCl₂). However, CWS combined with trivalent salt (AlCl₃) sharply increased the viscosity. The zeta potential of CWS with inorganic salts increased which can enhance the electric repulsion and beneficial to reduce the viscosity. The content of free water in CWS with trivalent salt decreased, and the freedom of the free water in CWS with trivalent salt decreased which were all bad to the viscosity and the adsorption of the dispersant on the particles. Compared with the surface polarity of the particles without inorganic salts, the surface polarity of the particles with divalent salts was similar to those without inorganic salts. Under the comprehensive influence, divalent salt has little effect on the viscosity of CWS.

Preparing coal slurry from coking wastewater to achieve resource utilization: Slurrying mechanism of coking wastewater-coal slurry

Coking wastewater is used to prepare coal slurry, which can be used as combustion and gasification fuel. This promising technology simultaneously achieves resource utilization and wastewater management. Slurrying properties are essential to the industrial application of coal slurry. These properties are considerably influenced by coal surface properties and the adsorption of an additive by coal. In this study, the effects of the internal components (e.g., phenol, ammonia nitrogen, and metal ions) of coking wastewater on the adsorption of an additive by coal and on coal surface properties were measured. Results showed that the competitive adsorption between phenol and the additive reduced the amount of additive adsorbed on coal. However, phenol acted as an additive to improve the wettability of coal particles. Cations (Ca²⁺, NH₄⁺, and Na⁺) adversely affected the slurrying because they weakened the negative charges of coal. Furthermore, a large amount of water was adsorbed due to the ionic bonding effects, thereby reducing the free water in the coal slurry system. The maximum slurrying concentration of CWCS was 0.8 percentage points higher than that of CWS, suggesting that coking wastewater enhanced the slurrying capability of the coal slurry by integrating the various effects induced by the different internal components.