Tianhua Yang

Transformation of apatite phosphorus and non-apatite inorganic phosphorus during incineration of sewage sludge.

The recovery of phosphorus from incinerated sewage sludge ash (SSA) is assumed to be economical. Transformation from non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP), which has a higher bioavailability and more extensive industrial applications, was studied at 750-950°C by sewage sludge incineration and model compound incineration with a calcium oxide (CaO) additive. Thermogravimetric differential scanning calorimetry analysis and X-ray diffraction measurements were used to analyze the reactions between NAIP with CaO and crystallized phases in SSA. High temperatures stimulated the volatilization of NAIP instead of AP. Sewage sludge incineration with CaO transformed NAIP into AP, and the percentage of AP from the total phosphorus reached 99% at 950°C. Aluminum phosphate reacted with CaO, forming Ca2P2O7 and Ca3(PO4)2 at 750-950°C. Reactions between iron phosphate and CaO occurred at lower temperatures, forming Ca(PO3)2 before reaching 850°C.

A new integrated evaluation method of heavy metals pollution control during melting and sintering of MSWI fly ash

Evaluations of technologies for heavy metal control mainly examine the residual and leaching rates of a single heavy metal, such that developed evaluation method have no coordination or uniqueness and are therefore unsuitable for hazard control effect evaluation. An overall pollution toxicity index (OPTI) was established in this paper, based on the developed index, an integrated evaluation method of heavy metal pollution control was established. Application of this method in the melting and sintering of fly ash revealed the following results: The integrated control efficiency of the melting process was higher in all instances than that of the sintering process. The lowest integrated control efficiency of melting was 56.2%, and the highest integrated control efficiency of sintering was 46.6%. Using the same technology, higher integrated control efficiency conditions were all achieved with lower temperatures and shorter times. This study demonstrated the unification and consistency of this method.

Kinetic study of heavy metals Cu and Zn removal during sewage sludge ash calcination in air and N 2 atmospheres

Heavy metal control is essential during the thermochemical recovery of phosphorus (P) from sewage sludge ash (SSA). For medium volatile heavy metals, i.e. Cu and Zn, the effect of chlorine additive was complicated and more sensitive to temperature variation. So, in the in-depth study on the removal kinetics of Cu and Zn was necessary. Thus, the studies described in this paper considered the experiments and kinetic models of Cu and Zn removal in SSA through calcination under different atmospheres and temperatures. The results showed that within 15 min, the removal of Cu and Zn was more effective at the same temperature in air than in N2. The result is consistent with kinetic analysis: Reaction activation energy of both Cu and Zn in an air atmosphere is lower than in N2. In addition, the reaction orders, energy and frequency factors of Cu and Zn removal reaction during SSA calcination at high temperature with air and N2 atmosphere were calculated.