A quadratic regression model on the removal of fluorine from tea soil

The fluorine in tea has become an important harassment on human health and the development of tea industry. Based on the single factor experiment, a quadratic regression model was established to optimize the removal of fluorine in tea soil by EDTA using orthogonal rotation combination design. The model was expressed as y = 62.92642－6.80471x1 + 2.85102x2 +3.74368x3－6.65557x12－4.74638x42 +2.70625x1x4 +2.70625x2x3, in which y is the potential removal rate of fluorine in tea soil, x1 is EDTA density, x2 is pH, x3 is SDS dosage, and x4 is F content in soil. The calculation results from the model showed that when EDTA density is 0.085 mol/L, pH value is 8.9, SDS dosage is 21.70 mL and F content in soil is 650.65 mg/kg, the yield(y) reaches the maximum (71.70％), which was confirmed by the experiment result.