No abstract

Ultrafine calcium carbonate is a widely used cheap additive. The research is conducted in low degree supersaturation solution in order to study the polymorphic phases’ change and its factors of the calcium carbonate precipitate in the ammonification-carbonization process of the solution with calcium. Fine particles of calcium carbonate are made in the solution containing 0.015 mol/L of Ca2+. Over 98% of the calcium carbonate precipitate without ammonification resembles the morphology of calcite, while the introduction of ammonia can benefit the formation of vaterite. It was inferred that the main cause should be serious partial oversaturation or steric effects. Ammonia also helps to form the twin spherical calcium carbonate. However, particles formed in the process of ammonification-carbonization in solution with low concentration degree of calcium are not even with a scale of the particle diameter from 5 to 12 μm. Inorganic salts, alcohol, or organic acid salts have significant controlling effect on the particle diameter of calcium carbonate and can help to decrease the particle diameter to about 3 μm. Anionic surfactants can prevent the conglobation of calcium carbonate particles and shrink its diameter to 500 nm–1 μm.

No abstract

No abstract

No abstract

No abstract

Three methods, sodium hydroxide hydrothermal treatment, sodium carbonate calcination-hydrothermal treatment, and sodium hydroxide calcination-hydrothermal treatment, were used to modify fly ash as an adsorbent for wastewater treatment. Results from XRD analysis show that the fly ash with sodium hydroxide hydrothermal treatment the fly ash has a porous structure in which alumina disappear and silica is dissolved. With sodium carbonate calcination-hydrothermal treatment exhibits nepheline and Na7Al7SiO16 structures. With sodium hydroxide calcination-hydrothermal treatment a zeolite-like new phase and porous structure can be observed. Results from SEM and BET indicate that the specific surface area increases from 0.160 m2/g for the raw material to 7.22 m2/g, 1.05m2/g and 276 m2/g for the respectively modified by sodium hydroxide hydrothermal treatment, sodium carbonate calcination-hydrothermal treatment and sodium hydroxide calcination-hydrothermal treatment. The three modified fly ash were used to treat a concentration of 80 mg/L of ammonia-nitrogen wastewater. The removal capacity for the three modified ash was 58%, 44% and 94% respectively that was significant higher than 14% for the original fly ash. These results show that fly ash by alkali modification can improve the activity and enhance the ability of ammonia-nitrogen wastewater treatment.

No abstract