Enhanced fluoride adsorption of aluminum humate and its resistance on fluoride accumulation in tea leaves.

Tea trees (Camellia sinensis) can take in fluorine from soil and the content of fluorine in tea increases with maturity, leading to high content of fluoride in tea leaves and tea products. Long-term consumption of high fluoride tea products could result in chronic fluoride intoxication. Confining the fluoride in the earth with absorbents to reduce the fluoride accumulation of the tea trees during the growth period which could radically control the fluoride level in tea product. Humic acid (HA), a kind of organic matter in the earth was used as raw material to prepare adsorbent aluminum humate (HAA) by aluminum modification. The HAA absorbent presented excellent absorption performance to the fluoride in a wide pH range (4-10), and the maximum adsorptive capacity can reach to 62.5 mg/g. The absorption isotherm demonstrated the adsorption of fluoride was the monomolecular adsorption and the absorption was in accordance with the pseudo-second order kinetic equation. Fluoride content in real soil solution decreased significantly by 53.03% by using the HAA absorbent. The utilization of HAA adsorbent in the culture and field plots experiments also obviously adsorb the soluble fluoride in solution and soil, which could significantly suppress the fluoride accumulation in tea leaves. In September, the fluoride accumulation in tea leaves has been reduced 74.29% in the field plots experiments.