Abstract
Nutrient pollution of surface water, such as excess phosphate loading on lake surface water, is a significant issue that causes ecological and financial damage. Despite many technologies that can remove available phosphate, such as material-based adsorption of those available phosphate ions, the development of a material that can trap them from the surface water is worth doing, considering other aspects. These aspects are: (i) efficient adsorption by the material while it settles down to the water column, and (ii) the material itself is not toxic to the lake natural microorganism. Considering these aspects, we developed a trace lanthanum-grafted surface-modified palygorskite, a fibrous clay mineral. It adsorbed a realistic amount of phosphate from the lake water (typically 0.13–0.22 mg/L). The raw and modified palygorskite (Pal) includes unmodified Australian Pal, heated (at ~400 °C) Pal, and acid (with 3 M HCl)-treated Pal. Among them, while acid-treated Pal grafted a lower amount of La, it had a higher adsorption capacity (1.243 mg/g) and a quicker adsorption capacity in the time it took to travel to the bottom of the lake (97.6% in 2 h travel time), indicating the adsorption role of both La and clay mineral. The toxicity of these materials was recorded null, and in some period of the incubation of the lake microorganism with the material mixture, La-grafted modified clays increased microbial growth. As a total package, while a high amount of La on the already available material could adsorb a greater amount of phosphate, in this study a trace amount of La on modified clays showed adsorption effectiveness for the realistic amount of phosphate in lake water without posing added toxicity.
Highlights
Nutrient pollution, in particular excess phosphorus (P) accumulation in lake surface water, is a serious problem for water quality, ecosystems, and healthy food chains [1]
When the clay is treated with La ions, it could raise toxicity concerns caused by the lanthanum [6]
We used an Australian fibrous clay mineral identified as palygorskite to be grafted with a low dosage of La, which could be efficient for the removal of phosphate and total phosphorous available in the real lake water
Summary
In particular excess phosphorus (P) accumulation in lake surface water, is a serious problem for water quality, ecosystems, and healthy food chains [1]. Modified clays became promising material technologies to serve the same purpose [3] Among those modified clays, lanthanum (La)-treated clay minerals have been deemed to be effective to remove P from its available form into a precipitated complex. We used an Australian fibrous clay mineral identified as palygorskite ( known as attapulgite) to be grafted with a low dosage of La, which could be efficient for the removal of phosphate and total phosphorous available in the real lake water. The toxicity of the whole composite material and the adsorption capacity of materials during the sinking time is important in terms of safe use of material These are critical gaps that need to be addressed by research experiments using real lake water, such as that used in the present study. The effect of various pre-treatment of Pal on the La grafting and thereafter adsorption of phosphate was tested in this study
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