Technosols in coal mining areas: Viability of combined use of agro-industry waste and synthetic gypsum in the restoration of areas degraded

This study assessed the viability of the combined use of coal processing waste (CPW), rice processing waste (RPW), poultry agro-industry sludge (PAS), synthetic gypsum (SG), topsoil (TS), and B horizon soil (BH) to reclaim areas degraded by coal mining. A Classification, Potentiality, Quantity/viability, and Application (CPQvA) systematic was employed to assess the feasibility of using these waste and materials to construct technosols. An experiment consisting of five technosols (T-1–T-5) was replicated four times in a completely randomized block design. Technosols fertility was analyzed 12 months after the establishment of the experiment. The mean fertility parameters, presented as mean ± 1 SD, were subjected to one-way analysis of variance, and the differences were tested using Tukey's test (P < 0.05). The results confirmed that RPW was the main source of Mg (1584 mg kg−1), K (1955 mg kg−1), Mn (708 mg kg−1), and Fe (1511 mg kg−1); PAS was the main source of Organic Matter (OM) (465 g k−1), N (42 g k−1), Al (2880 mg kg−1), and Zn (394 mg kg−1); while SG was the main source of Ca (30,494 mg kg−1). The T-4 and T-5 technosols, composed of equal amounts of SG + RPW + PAS and TS + SG + RPW + PAS, respectively, presented the best fertility results, with the higher mean values of K (96.3 ± 19.6 mg dm−3), Ca (1044 ± 165 mmolc dm−3), OM (62 ± 14 g kg−1) and cation exchange capacity (CEC) (1066 ± 168 mmolc dm−3) observed in T-4, and P (40.4 ± 12.6 mg dm−3) in T-5. Notably, T-4 did not include TS in its composition, which is important because it does not require commissioning of natural areas to reclaim degraded areas. Each hectare of 0.2 m of T-4 would cost USD 23,291.64, considering just the waste transporting costs. The results demonstrate the feasibility of the combined use of waste tested in this study to reclaim degraded areas by coal mining.