Removal of cationic and anionic textile dyes with Moroccan natural phosphate

Moroccan natural phosphate was tested as an effective adsorbent for the removal of cationic dye rhodamine 6G (Rh6G) as well as anionic dye congo red (CR) from wastewater. The X-ray diffraction, FTIR and EDX characterizations reveal that the sample contains 98 wt% fluoroapatite (Ca-5(PO4)(3)F) with 1 wt% quartz (SiO2) and 1 wt% calcium carbonate (CaCO3). Nitrogen sorption analysis shows that the BET specific surface area (S-BET) and BJH pore volumes of the sample are 18.8 m(2)/g and 0.1 cm(3)/g, respectively. Batch adsorption experiments of the dyes from aqueous solution were conducted, taking into account the influence of initial dye concentration (100-400 mg/L), adsorbent dosage (1-20 g/L), contact time (5-300 min) and solution pH (3-12). The Langmuir isotherm model best represents the equilibrium adsorption process of the two dyes. The calculated maximum adsorbed quantity q(max) of CR and Rh6G at dosage 20 g/L and pH value of 5.2 were found 19.81 and 6.84 mg/g, respectively. The adsorption of Rh6G and CR on natural phosphate was found to follow the pseudo-second-order model. Natural phosphate was also tested as an effective adsorbent for a simulated dye effluent under industrial conditions of temperature and pH. Desorption studies were conducted using HCl as an eluent and the highest elution efficiency for both dyes was obtained with a 0.1 M solution. Accordingly, it is demonstrated in this work that natural phosphate is a very efficient adsorbent for both cationic and anionic dyes from contaminated water, and represents a great low-cost alternative to commercial adsorbents due to its abundance as a natural resource in Morocco.