Separation of vivianite from digested sludge by flotation using oleic acid as a collector

The recovery of vivianite from anaerobically digested sludge has significant engineering implications for phosphorus recovery. Current phosphate recovery technology recovery technology has not yet reached a mature stage, and the complex process flow and equipment requirements make the investment and operating costs high. This study achieved the flotation separation of vivianite from digested sludge using collectors (oleic acid, surfactant, and sodium oleate) and an inhibitor (sodium silicate). The process involved investigating the adsorption of vivianite by the collectors and the inhibition of quartz in the sludge by the inhibitor. It has been found that the functional group of oleic acid can strongly adsorb onto the surface of vivianite, leading to an increase in its contact angle from 30.7° to 104.4° and significantly enhancing its hydrophobicity. This improvement facilitated the vivianite's attachment to foam, enabling effective separation from the sludge and quartz. Oleic acid exhibits the most significant shift towards a negative charge on the surface of vivianite and provides the best effect. Sodium silicate can effectively enhance the hydrophilicity of quartz in sludge, reducing the contact angle from 64.4° to 7.1°. This makes the quartz less likely to float and easier to separate from vivianite. Using 5 ml/L of oleic acid as the collector and 15 g/L of sodium silicate as the inhibitor, the recovery efficiency of vivianite can reach 67.8 %. This demonstrates that the flotation technique can effectively enrich vivianite in digested sludge.