Minimization of heavy metal containing sludge and recovery of metals from waste water by adsorption using activated diatomite

In this study, natural diatomite with high specific surface area and high permeability was used as an adsorbent to reduce the heavy metal containing sludge and recover copper from waste water. The original diatomite was wet chemically activated with hydrothermal sodium hydroxyl. After activating, the zero point of charge on diatomite surface increased from pH2 to pH3.5 and the surface potential reduced from-40mV to-60mV in the natural condition. The reducing of surface potential value is beneficial for the adsorption of cations onto the diatomite surface. Under the SEM observations, the original diatomite possesses porous structure clearly and the surface area is up to 50.26 m²/g. By alkali etching, the specific surface area of the diatomite after activation changed to 38.45 m²/g. The adsorption experiments show also that the adsorption capacity for copper in water of activated diatomite was 3 times higher (36.5 mg/g) than the original one (12.6 mg/g). This could be applied to reduce the heavy metal containing sludge in waste water treatment. By using adsorption technology with activated diatomite as post-treatment, the chemical dosage in the precipitation process can be reduced which leads also to the minimization of sludge production. Furthermore, the adsorbed heavy metal such as copper can be recovered by the regeneration of diatomite adsorbent as well.