Iron hydroxide works as an adsorbent for some metal ions such as arsenic and selenium and is used as a scavenger. In this study, the removal of fluoride in solution by ferric hydroxide powders has been investigated. Ferric hydroxide powders were prepared by adjusting pH in four kinds of ferric salt solutions to 3.0 followed by filtration and drying. Ferric chloride, ferric nitrate, ferric sulfate and ferric polysulfate were used as ferric salts. All the ferric hydroxide powders removed fluoride ions in the pH range between 6.0 and 7.0. Ferric hydroxide powder formed in ferric polysulfate solution was the most efficient. Sulfuric ion concentration increased with increase in the adsorbed amount of fluoride ions. It is known that sulfate ions adsorb on the surface of ferric hydroxide that precipitate in sulfuric solution. Fluorite ions could be removed by ion exchange with sulfate ions on the surface of ferric hydroxide.
Moringa oleifera (M. oleifera) is one of the most widely spread Moringa species that grows quickly in the tropical belt. The objective of this study was to investigate the influence of the aqueous pH, initial turbidity of the synthetic kaolin turbid water, ionic strength, and humic substances on the efficiency of the M. oleifera coagulant. The experimental results showed that the coagulation efficiency was significantly enhanced by the presence of divalent cations such as Ca2+ or Mg2+, and slightly enhanced by lowering the aqueous pH from 9.0 to 4.0. It was also found that fulvic acid did not significantly affect the coagulation efficiency, while the initial turbidity and humic acid did. M. oleifera coagulant was effective for synthetic waters of an initial turbidity of 290 NTU. However, turbidity removal was not observed when the initial turbidity was lowered to 45 NTU. The presence of humic acid significantly increased the coagulant dosage required for turbidity removal. These obtained experimental observations were then used to discuss the influence of the water quality on the dominant coagulation mechanism.
A liquid-liquid separation method using aqueous and oil phases has been put forward for separation of fine zircon-alumina mixtures to recycle abrasives waste. By using a cation surfactant, zircon particles were made hydrophobic and extracted into the oil phase, whereas alumina remained in the aqueous phase. In this way, the fine zircon-alumina mixtures could be well separated. The result confirmed that the liquid-liquid separation method can be used to separate the fine zircon-alumina mixtures achieving relatively high grade and recovery.