Abstract
Ash from poultry feather gasification was investigated as an adsorbent for Cd removal from synthetic wastewater under a range of operational conditions: initial pH (2–8) and salinity (8–38 mS/cm) of wastewater, ash dosage (2.5–50 g/L), Cd concentration (25–800 mg/L) and contact time (5–720 min). The ash was highly alkaline and had low surface area and micropores averaging 1.12 nm in diameter. Chemical/mineralogical analysis revealed a high content of P2O5 (39.9 wt %) and CaO (35.5 wt %), and the presence of calcium phosphate, hydroxyapatite and calcium. It contained only trace amounts of heavy metals, BTEX, PAHs and PCBs, making it a safe mineral by-product. Cd adsorption was described best with Langmuir and pseudo-second order models. At pH 5, an ash dosage of 5 g/L, 40 min contact time and 100 mg Cd/L, 99% of Cd was removed from wastewater. The salinity did not affect Cd sorption. The maximum adsorption capacity of Cd was very high (126.6 mg/g). Surface precipitation was the main mechanism of Cd removal, possibly accompanied by ion exchange between Cd and Ca, coprecipitation of Cd with Ca-mineral components and Cd complexation with phosphate surface sites. Poultry ash effectively removes high concentrations of toxic Cd from wastewater.
Highlights
Heavy metals are commonly found in industrial wastewater from mining, electroplating, metallurgy and chemical plants [1]
Physical analyses: The Brunauer-Emmet-Teller (BET) specific surface area was determined by fitting the BET equation to the linear portion of the BET plot; the pore size distribution was calculated on the basis of the desorption plot of the N2 adsorption-desorption isotherm using the Barret-Joyner-Halenda method (Micrometrics ASAP 2000, USA)
Most of the particles were irregular in shape, with the presence of aggregate-like structures that could be carbonaceous in nature (Figure 3a,b) and microflake structures (Figure 3c,d)
Summary
Heavy metals are commonly found in industrial wastewater from mining, electroplating, metallurgy and chemical plants [1]. They pose a threat to the environment due to their toxicity, non-biodegradability, persistence and bioaccumulation at low concentrations [2]. It is thought that the largest anthropogenic source of Cd released to aquatic environments is the smelting of non-ferrous metal ores [3]. This metal is used to make Ni-Cd batteries, pigments, phosphate fertilizers, alloys and metal plating [4]. There are technological reasons why heavy metals need to be removed from wastewater, as they can interfere
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