Two-Step Flotation Treatment for Removal of Toxic Matter from Hospital Solid Waste Incinerator Fly Ash

Abstract

Application of two-step flotation for removing dioxins and heavy metals from hospital solid waste incinerator (HSWI) fly ash was studied. In the first step, decarburization flotation was executed to remove dioxins from raw fly ash. The second step of precipitation flotation was carried out to recycle the toxic metals in the residual slurry. Finally, an acid leachingsulphide precipitation-flotation method was proposed. The results showed that carbon removal rate was 90.7%, and the dioxin removal percentage was 91.0% during decarburization flotation. And Zn, Pb and Cu in residual slurry were acidleached with the removal efficiencies being 91.3%, 79.2% and 85.6%, respectively. The optimum sulphidation condition of heavy metals in the residual slurry were Na 2 S molar ratio of 1.4 and sulphidation time of 30 min. Subsequently, precipitation flotation could recover 49.9% of Zn, 42.0% of Pb and 48.7% of Cu from the raw fly ash. After the two-step flotation, the toxicity of the tailings reduced considerably, and the tailings could be disposed in landfill. Therefore, this twostep flotation treatment of HSWI fly ash may result in both detoxification and potential resource recovery.

Cement solidification of the tailings after flotation of medical waste incinerator fly ash

“…Ash sample was dried for 24 h under the atmosphere of 383 K before the subsequent operation. Part of fly ash was treated with flotation column with 30 mm in diameter and 950 mm in height [17]. Compressed air (0.06 m 3 /h) was introduced into the column through a rotameter.…”

Characteristics and Treatment Methods of Medical Waste Incinerator Fly Ash: A Review

“…ALP can facilitate the separation and recovery of heavy metals from fly ash together with other post-treatment, such as thermal treatment, melting, solvent extraction, sulfidation precipitation, flotation, and immobilization treatment [1,61,63]. Many kinds of lixiviants have been applied in the ALP process: organic acids, such as tartaric acid, acetic acid, oxalic acid, and citric acid; inorganic acids, such as HNO 3 , HCl, and H 2 SO 4 ; chelating reagents, such as diethylenetriaminepentaacetate, ethylendiaminetetraacetate, and nitrilotriacetic acid; and alkaline lixiviants, such as sodium hydroxides and ammonium salts.…”

“…A novel process for the successive removal of dioxins and recovery of heavy metals from MWIFA was also developed by Wei [42]. Thereafter, by the process of acid leaching-sulfidation and precipitation-flotation, 42.0% of Pb, 48.7% of Cu, and 49.9% of Zn could be recovered [1]. Furthermore, the destruction efficiencies of dioxins in the froths could exceed 98% at above 1000 • C after reburning treatment of the froths, so it seems that recirculation of froths in the incinerator can serve the dual purpose of destruction of dioxins and energy recovery of carbon constituents [42].…”

“…Medical waste incinerator fly ash (MWIFA) refers to a kind of incineration residue accounting for approximately 3-5 wt.% total mass of the original waste, which is collected by the bag filter of the waste incineration system [1]. MWIFA contains high levels of dioxins, leachable alkali chlorides, carbon constituents, and heavy metals.…”

Recovery of Residual Carbon from Ti-Extraction Blast Furnace Slag by Flotation with Simultaneous Dechlorination

“…Wang et al conducted a study on the flotation dynamics of low-rank coal with collector agents; compared with a single collector, the mixed collector could accelerate the coal particle aggregation and increase the particle-bubble attachment index [31]. The flotation machine's impeller stirs the waste and water sufficiently, where the harmful substances, heavy metals, and soluble salts are dissolved in the water, thus reducing the harmfulness of the waste and improving its availability [32,33]. Based on the above studies, it is feasible to recover carbon residue and dechlorination from EBFS by froth flotation.…”