Objective Composts can supply nutrients and potentially ameliorate acidic soils; however, systematic evidence on how to enhance their acid-buffering capacity remains limited. This study investigated how inorganic mineral amendments influence the acid-buffering capacity and maturity characteristics of chicken manure–wheat straw compost, with the aim of improving both composting efficiency and the potential for soil acidity neutralization.

Methods A 75-day aerobic composting experiment was conducted using chicken manure and wheat straw under four treatments: an unamended control (CK), phosphogypsum addition (PG), phosphogypsum plus attapulgite (PP), and attapulgite plus magnesium sulfate (PM). Compost products were characterized by pH, electrical conductivity, acid neutralization capacity, carbonate content, surface functional groups, thermal stability, and mineral composition to evaluate the effects of mineral amendments on acid-buffering capacity and maturity.

Results Compared with CK, both PG and PP significantly decreased compost pH and acid neutralization capacity, whereas PM showed pH and acid neutralization capacity comparable to CK, indicating that phosphogypsum weakened the acid-neutralizing ability of the compost. X-ray diffraction revealed that calcite (69%) and struvite (23%) were the major crystalline phases associated with acid neutralization in CK. The acidic phosphogypsum markedly reduced the relative contents of calcite and struvite in PG and PP, while struvite was the dominant mineral phase in PM (47%). Fourier-transform infrared spectroscopy indicated higher aromaticity in CK, PG, and PP; by contrast, PM exhibited lower aromaticity but contained more carboxyl, hydroxyl, and amino functional groups. Thermogravimetric analysis combined with X-ray diffraction suggested that PM retained partially crystalline cellulose and showed a lower degree of decomposition, whereas CK, PG, and PP were more decomposed and thermally stable.

Conclusions The combined addition of phosphogypsum and attapulgite enhanced the thermal stability of the compost, but the incorporation of phosphogypsum inhibited the formation of calcite and struvite and reduced the acid neutralization capacity of the compost product. In contrast, the combination of attapulgite and magnesium sulfate maintained or enhanced acid-neutralization capacity by promoting struvite formation and enriching organic functional groups. Overall, our findings demonstrate that inorganic mineral amendments differentially regulate compost acid-buffering capacity and quality through coupled controls on mineral phases and organic functional groups, providing a mechanistic basis for formulating high-quality organic fertilizers with both nutrient-supply and acid-buffering functions.