Application of crushed shells Cristaria plicata to separation cadmium and chromium from polluted water by static sorption

Abstract

Cristaria plicata is a species of freshwater mollusk in the genus Cristaria of the family Unionidae. Cristaria plicata shells are available natural raw materials in Vietnam for the production of sorbents that can absorb many pollutants from wastewater. The most important pollutants are heavy metals. The aim of the study was to study the possibility of using powders from Cristaria plicata shells to purify contaminated water from heavy metals such as Cd and Cr by sorption method. A technology for obtaining a sorbent has been developed. After collection, the shells were washed, dried and ground to a size of no more than 0.5 mm, then the powder was soaked in distilled water for 10 hours, dried to a constant weight and sieved through sieves, collecting a fraction with a particle size of about 0.5 mm. Microscopic studies showed that the sorbent parti-cles from the shells of Cristaria plicata contained pores with a diameter of 4.5 to 8.2 microns and a length of 15.9 to 27.6 microns. The static sorption method was used. The Cd and Cr content in water samples before and after sorption was performed by atomic absorption spectrophotometry. It is shown that the sorbent from the shell material of Cristaria plicata can be used quite effectively for wastewater treatment from Cd and Cr. It was found that with an increase in the mass fraction of the powder in the treated water, the concentration of Cr and Cd in this water noticeably decreases. The Cr content drops by 29.5-45.5% after shaking for 60 minutes, while the Cd content drops by 91.6-96.9%. The absorption capacity of the sorbent from the shells of Cristaria plicata depends on the initial concentrations of Cr and Cd, the higher the initial concentration, the more pollutants are absorbed by the sorbent. The best effect of sorption purification is observed at the initial concentrations of Cd 1 mg/l and Cr 20 mg/l. For maximum Cd allocation, the recommended processing time is 40÷60 minutes, and for Cr-80÷100 minutes.