Leaching behavior of phosphorous compounds from sewage sludge ash based on quantitative X-ray diffraction analysis

Abstract

Phosphorus (P) is an essential and limited resource. Incineration sewage sludge ash (ISSA) contains a high amount of P, which can be recovered using chemical leaching methods. However, the recovery ratio depends on the speciation of P and the leaching conditions. In this study, hydrochloric acid was used as a leaching agent, and the effects of the hydrochloric acid concentration, leaching time, temperature, and liquid-solid ratio on the P leaching ratio were investigated. Furthermore, the co-leaching of macro-metals Ca, Al, Fe, and Mg was analyzed. The results showed that P leached rapidly within 30 min, where the leaching rate reached more than 80% and then gradually stabilized. The leaching concentrations of Ca and Mg had a significant correlation (correlation coefficient r 2 > 0.90), and both were leached completely. Al and P had similar leaching patterns, where the leaching rates increased initially and then decreased with time at 0.2 mol/L HCl. According to X-ray diffraction analysis and Rietveld refinement, the P in ISSA was mainly present in the forms of Mg 3 Ca 3 (PO 4) 4 and AlPO 4. When leached using 0.2 mol/L HCl at 55 °C with a liquid-to-solid ratio of 20 L/kg, the AlPO 4 and Fe 3 (H 2 O) 3 (PO 4) 2 in ISSA dissolved initially and then precipitated on the surface of the solid phase, thereby impeding further P leaching.

Extraction and Purification of Phosphorus from the Ashes of Incinerated Biological Sewage Sludge

“…It is reasonable to assume that at pH 3.7, the precipitation of Ca 3 (PO 4 ) 2 , FePO 4 , and AlPO 4 sequestered P from the solution, reducing its extraction yield. This result is consistent with the finding of He et al [55]. Although at this pH range, P occurred in several forms (including H 2 PO 4 − and HPO 4 2− ), it precipitated in the form of complex phosphates [56].…”

Molybdenum Nitrides, Carbides and Phosphides as Highly Efficient Catalysts for the (hydro)Deoxygenation Reaction

“…[2] Over the last decade, research into the catalytic HDO of SA has mainly involved the use of metals in a reduced state (Pt, Pd, Co, Ru, Ni) or of bimetallic sulfides (NiMoS 2 , CoMoS 2 ) on various supports. [11][12][13][14][16][17][18] However, the corrosiveness of sulfurcontaining catalysts had led to attention being focused on the use of Ni-and Pd-containing catalysts. The most promising of these, 5 wt.% Ni supported on γ-Al 2 O 3 , SiO 2 or HÀ Y-80, achieved 100% conversion of SA in the deoxygenation reaction after 6 h at 300°C and under a hydrogen pressure of 30 bar.…”

Extraction of Phosphorus from Sewage Sludge Ash—Influence of Process Variables on the Electrodialytic Process

“…Al and Ca were included because of their expected importance for the process. The importance of Al in acid extraction processes was e.g., reported in [22] where they identified AlPO 4 in the SSA, which was partly dissolved in HCl and then precipitated again on the surface of the solid phase. Ca has been shown to represent a significant mass percentage in the SSA, and calcium phosphates have been identified in SSAs (also in SSAs from the same incineration plant [15]).…”

“…The finding that the 2C-ED extraction process was most efficient at a high L:S ratio is contrary to findings for batch acid extractions. Here, the leaching of P increases with the L/S ratio [22]. A low L:S ratio during 2C-ED is desirable since the two factors, L:S and duration, determine a treatment plant's size.…”