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Preparation of amphoteric modified bentonite from calcium-based bentonite for adsorption of anionic dye. The importance of sodium-modification pretreatment

Yin Hang, Ren Zijie, Gao Huimin, Han Weiyi, Guan Junfang

Physicochemical Problems of Mineral Processing

2021

Vol. 57, iss. 1

1--17

To understand the influence of sodium-modification pretreatment on the adsorption of anionic dye by amphoteric modified bentonite, three kinds of adsorbent materials, including sodium-modified bentonite, amphoteric modified calcium-based bentonite and amphoteric modified bentonite pretreated by sodium modification, were firstly synthesized and characterized, and afterwards their adsorption performance and mechanism for a form of anionic dye, Acid Yellow 11, were investigated comparatively. The crystalline phases, hydration property, surface charge characteristic and functional groups of prepared modified bentonite were characterized and evaluated by X-ray diffraction swelling volume, Zeta potential and Fourier transform infrared spectroscopy, respectively. The sodium modification expanded the interlayer space of montmorillonite, released the internal surface area and improved the hydration performance of bentonite. Due to the replacement of Na+ for Ca2+, the probability of interlayer cations overflowing from the interlayer space and exchanging with the amphoteric modifier increases. Therefore, the content of interlaminar organic material in amphoteric modified bentonite pretreated with sodium-modification pretreatment was higher than that in unpretreated amphoteric modified bentonite. The hydration and dispersibility were significantly stronger, and the adsorption capacity of acid dye was also better. The findings of this investigation suggest that sodium modification pretreatment is very positive and necessary in the process from sodium–amphoteric modification.

Selective flotation of witherite from calcite using potassium chromate as a depressant

Qiu Yangshuai, Zhang Lingyan, Jiao Xuan, Guan Junfang, Li Ye, Qian Yupeng

Physicochemical Problems of Mineral Processing

2019

Vol. 55, iss. 2

565--574

Witherite has been widely used as an industrial and environmental source of barium, with calcite being the primary associated carbonate mineral. However, few studies have been conducted to effectively concentrate witherite from barium ores. In this work, with the treatment of potassium chromate (K2CrO4) and sodium oleate (NaOL), witherite was selectively separated from calcite through selective flotation at different pH conditions. In addition, contact angle, Zeta potential, adsorption and X-ray photoelectron spectroscopy measurements were performed to characterize the separation mechanisms. The results demonstrated that NaOL had a strong collecting ability for both witherite and calcite; nevertheless, witherite could be effectively selected from calcite with the highest recovery at pH 9 in the presence of K2CrO4. From the XPS measurements, NaOL and K2CrO4 were found to be primarily attached to the surfaces of witherite and calcite through chemisorption. The presence of K2CrO4 on the surface of calcite adversely influenced the NaOL adsorption, which could make the flotation separation efficient and successful.