Spray-Dried Clay Powders vs. Ammonium Pollution. 水中「汚染物」アンモニウムイオンに対して粘土粒子の吸着力は?

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Adsorptive Capacity of Spray-Dried pH-treated Bentonite and Kaolin Powders for Ammonium Removal. pH調整した噴霧乾燥による粘土系粒子ベントナイトおよびカオリンのアンモニウム吸着能力
Permanent link: https://doi.org/10.1016/j.apt.2021.02.036

肥料が豊富な農地からの流出はアンモニウム(NH4+)汚染の大きな発生源の一つである。湖や水流における高濃度のNH 4+は富栄養化を引き起こし、藻類の異常発生や水中の溶存酸素の枯渇をもたらす。汚染物質の除去や無害化のために、化学処理剤の代わりには、フィトレメディエーション(phytoremediation、植物による環境修復)のような、持続可能な新しい戦略が注目されている。フィトレメディエーションにおけるコストの面では粘土吸着アプローチが有望である。粘土は豊富に存在するうえ、無毒性であり、植物の成長を促進するなどポテンシャルが高い。本研究では、粘土粒子に対して噴霧乾燥法を試み、原料のpHを変化させて粘土粒子の表面電荷を調整し、得られた粉末のアンモニウム吸着能力を調べた。代表的な粘土系材料であるベントナイトとカオリンを用い、粘土粒子の表面形態、表面電荷、元素組成、結晶度のような物理化学的なパラメータに注目した。最も高い吸着容量は、高pHで処理したベントナイトにより得られ、Langmuirの吸着等温線モデルに従うことも確認された。

責任著者:Wuled Lenggoro

所属:東京農工大学 工学部 化学物理工学科

E-mail:wuled(@)cc.tuat.ac.jp

A main source of water pollution is run-off from agricultural sites. Agricultural run-off is still considered amongst the most important producers of ammonium pollution. The high concentration of NH4+ in lakes or water streams can cause eutrophication, which results in algal bloom and depletion of dissolved oxygen in water [4]. NH4+ can be toxic and dangerous to health when the concentration in the human body exceeds 200 mg per kg of body weight. The presence of NH4+ in water also causes several other problems, such as creating an odour, forming nitrites in the water supply system, impairing manganese removal, and reducing disinfection efficiency. Novel, cost-effective, and sustainable remediation strategies, such as phytoremediation, are needed to substitute various chemical treating agents towards the removal or detoxification of contaminants.。

Using clay adsorption to support phytoremediation is a promising approach to solve the cost issue. Other advantages of clay (bentonite, kaolinite, etc.) include abundant availability, non-toxicity, high adsorption capacity and large potential for ion exchange, promoting plant growth.

The objective of our study was to evaluate the NH4+ adsorption capability of bentonite and kaolin and their spray-dried powders by adjusting their surface charge under various pH conditions. The zeta potential value of the clays was varied to evaluate their adsorption capacity. The effect of treatment time and clay dosage, as well as the adsorption isotherm were also investigated to better understand the adsorption behavior.

Examination of several physicochemical parameters, such as the surface morphology, surface charge, elemental composition and the crystallinity of the clay particles, was used to validate the efficiency of the treatment. Results showed that bentonite adsorption capacity was enhanced by high pH treatment and it was fitted well by the Langmuir isotherm equilibrium model.

課題:水中のアンモニウムイオンの除去

手法:天然粘土(粉末)に処理プロセスを施す

HIGHLIGHTS

For ammonium removal, spray-dried pH-treated clays as adsorbents were prepared.

Adsorption capacity was examined after up to 2 h of sample exposure.

Adsorption isotherm for bentonite showed a fit with Langmuir model.

pH 10-treated (and as-received sample) bentonite showed the highest adsorption capacity.

Abstract

The effectiveness of ammonium (NH4+) adsorption was investigated, using spray-dried, pH-treated bentonite, and kaolin as adsorbents. Each powder’s adsorption capacity towards NH4+ was examined after up to 120 min of sample exposure, and results were compared. The zeta potential values for bentonite samples were between −1.1 and −19.4 mV, while for kaolin samples, they were between −35.7 and −40.9 mV (pH range examined was 2–10). The adsorption isotherm for bentonite showed a fit with the Langmuir model. The pH 10-treated bentonite and as-received bentonite (dispersed as pH 10 in distilled water) showed the highest adsorption capacity towards NH4+. Meanwhile, for kaolin, the adsorption capacity was low and observed only at low NH4+ concentration (100 mg/L and 200 mg/L), with pH 10-treated kaolin showed the highest adsorption capacity. 吸着剤を想定する応用として、噴霧乾燥とpH処理されたベントナイトおよびカオリンを用い、アンモニウム (NH 4+)に対する吸着の有効性を調べた。NH4+に対する各サンプル粉末の吸着容量を120分までの曝露実験後に調べた。ベントナイト試料のゼータ電位値は−1.1から−19.4 mVの間であったが、カオリン試料では−35.7から−40.9 mVの間であった。調べたpH範囲は2から10であった。ベントナイトの吸着等温線はLangmuirモデルと一致した。pH10で処理したベントナイト(及び受け取ったままの)ベントナイト (蒸留水中にpH 10で分散) はNH 4+に対して最も高い吸着容量を示した。一方,カオリンについては吸着容量は低く,低いNH 4+濃度 (100 mg/Lと200 mg/L) でのみ観察されるが、カオリンの場合もpH 10で処理した試料は最も高い吸着容量を示した。

AUTHORS:

Nurul Solehah Mohd Zaini (was a visiting grad. student from UPM), Wuled Lenggoro, Mohd Nazli Naim (TUAT alumnus at UPM), Norihiro Yoshida (Grad. student TUAT), Hasfalina Che Man, Noor Fitrah Abu Bakar, Siti Wahidah Puasa.

INSTITUTIONS

Graduate School of Bio-Applications and Systems Engineering, Department of Applied Physics and Chemical Engineering, and Institute of Global Innovation Research, Tokyo University of Agriculture and Technology (TUAT)

Department of Process and Food Engineering, and Department of Biological and Agricultural Engineering, Faculty of Engineering, Universiti Putra Malaysia

Faculty of Chemical Engineering, Universiti Teknologi MARA, Malaysia

研究室の発表論文の紹介(Introduction of papers from our group) >> https://tag/paper/