Removal of fluoride by nature diatomite from high-fluorine water: An appropriate pretreatment for nanofiltration process

• NF product water can't meet the standard sometimes.
• Chose diatomite to adsorb fluoride prior to nanofiltration process
• The characterization of nature diatomite
• The influences of pH, ionic strength, anions and organic matter
• The combination of adsorption process and NF treatment

Nanofiltration (NF) is an effective technology for fluoride rejection in drinking water which has characteristics of high water flux, high water recovery rate and low operation pressure, etc. However, high fluoride concentration severely influences the quality of its product water. Herein, nature diatomite was chosen to adsorb fluoride prior to NF process. The characterization of diatomite was investigated by SEM and XRD, and the feasibility was studied by XPS and FT–IR. The influences of diatomite dosage, pH, ionic strength and anions concentration were researched by batches of adsorption experiments. The presence of HA enhanced the adsorption of fluoride at pH < 5 while reduced fluoride adsorption at pH > 5. The adsorption process fitted the Langmuir isotherm and the adsorption kinetics fitted the pseudo-second-order rate equation. In addition, the combination of adsorption process and NF treatment was studied, which confirmed that the nature diatomite can ensure the permeate water of the NF system to meet the standard. Results of this study demonstrated that the nature diatomite was viable and effective to be used as the pretreatment adsorbent for NF system to defluorinate high fluoride water.