Utilisation of ultrasonic treatment to improve the soil amelioration property of coal fly ash

Fly ash application impacts master physicochemical pedovariables: A multilevel meta-analysis

Fly ash (FA) is a very alkaline, hazardous waste with a potential to be recycled in amelioration of master pedovariables, notably: i) pH, drives soil biogeochemistry, ii) electrical conductivity (EC), reflects soil salinity level and overall soil health, iii) water holding capacity (WHC), determines soil hydraulic functions and iv) bulk denisity (BD), indicates soil compaction and water-air relations. We performed a multilevel meta-analysis, encompassing 30 out of 1325 screend studies, using a random effect model and non-aggregated data sets. By moderating; experimental type, FA application rate, soil type and land use, two distinct meta-analytical approaches on observed pedovariables were performed: i) uni-moderator, considering moderators separately, and ii) multi-moderator, considering moderators combined. It was found that FA application: increased soil pH by 15.4% (Hedge's g = 8.07), EC by 51.7% (Hedge's g = 8.07), WHC by 22.6% (Hedge's g = 7.79), and reduced BD by 13.5% (Hedge's g = -5.03). However, the uni-moderator meta-analytical model revealed a significant increase in pH and EC only with relatively lower FA dosage (up to 20%). In addition, the impact of FA on pH and EC was significantly positive in acid (pHH2O < 6.5), negative in alkaline (pHH2O > 7.2), and not significant in neutral (pHH2O = 6.6-7.2) soil types. The same uni-moderator approach revealed that FA dosages above 5% significantly increased WHC, but reduced BD. Moreover, the multi-moderator model identified two significant interactions: i) between varying FA dosage and land use, and ii) between varying FA dosage and soil type. Confirmed positive implications of FA on key soil properties underscore its strong potential as a valuable resource for sustainable soil management, mitigating widespread soil constraints and contributing waste reduction. However, careful consideration of FA dosage, soil type, and land use is imperative to optimize FA application and prevent potential adverse environmental implications.

The possible application of fly ash (FA) to ameliorate acid mine water (AMD) for irrigation of potato (Solanum tuberosum L.)

Some areas in Johannesburg abounds with mine wastes namely, acid mine drainage (AMD) as well as fly ash (FA), which are by-products of gold mining and coal burning, respectively. Studies show that a solution formed through mixing these wastes neutralises the acidity of AMD and is an alternative source of irrigation. While studies show improved growth and yield of plants irrigated with fly ash-amended AMD, there are rarely sufficient studies conducted in South Africa showing evidence of altered pH of AMD and that food crops irrigated with fly ash-amended AMD exhibit improved concentration of essential nutrient elements. In this study, AMD was sourced from a gold mine in Johannesburg and fly ash collected from a coal-burning power station in the Mpumalanga Province, mixed at 1:0, 1:1, and 3:1 (w/v) of fly ash to AMD and used to irrigate potatoes. The objective was to assess whether the solutions of FA-amended AMD alter the pH of the AMD and to evaluate if irrigating potatoes with the aforementioned improve the concentration of essential nutrient elements and heavy metals in the tubers. Results show that the pH of AMD was increased in the 1:0 and 1:1 solutions but decreased in the 3:1 solution. The concentrations of Pb and Co were decreased in tubers irrigated with the 50 % AMD and 75 % AMD while that of Ni and Cd were markedly increased in tubers irrigated with solutions of fly ash-amended AMD. In the main, the potato tubers exhibited significantly higher concentrations of Al, Mo, Cu, Ca, Mg, and Zn when irrigated with fly-ash-amended AMD. The pH range levels from FA-AMD treated samples were within the acceptable pH range (5.5-6.5) which is acceptable for water that could be used for irrigation of crops. Also, the decreased Co and Pb and improved concentration of essential nutrient elements indicate that the constituents absorbed large quantities of the heavy metals while releasing the nutrients. In conclusion, the selected fly ash has proven as an alternative low-cost readily-available, affordable, and accessible adsorbent that neutralize the acidity of AMD, decrease the concentration of heavy metals, and increase the concentration of essential nutrient elements. Importantly, the liming potential among other traits of the fly ash improved the quality of the AMD such that the wastes were proven in this study suitable to irrigate potatoes.

Performance and mechanisms of alkaline solid waste in CO2 mineralization and utilization

CO2 mineral sequestration using alkaline solid waste (ASW) is a promising strategy for synergistically reducing CO2 emissions and reusing industrial waste. However, improvement the carbonation degree still remains challenges due to the sluggish leaching rate of Ca/Mg ion at low pH. To the issues, this study proposed an amine-mediated CO2 absorption and mineralization process with six common ASWs, as well an ecological utilization route of CO2-ASW productions. Experimental results indicated that calcium carbide slag (CS) had greater CO2 mineralization capacity (86.2 g-CO2/kg-CS) than other ASWs, while stirring rate and particle size played a more important role during CO2 capture. Amine-mediated CO2 capture was verified to be more excellent with steel slag (SS) as mineral medium. When the MEA concentration was increased to 2 mol/L, the extraction efficiency of Ca2+ was increased by 35 %, leaded to the CO2 removal efficiency significantly promoted from 49 % to 92 %. The characterization of structural morphology referred spherical aragonite or needle-bar calcite was dominant for the porous mineralization products (30.6 m2/g). High germination index of pea seed (112.1 % at a dose of 10 g/L) inferred the negligible toxicological effects of tiny MEA residue over SS mineralization products, after centrifugally washing treatment. Pea seeds cultivated with mineralized products after centrifugal washing can achieve a growth rate of about 4 mm/d. Overall, this work provides a feasible route to apply the porous CO2-ASWs production into water conservation in arid and sandy land.

Differential responses of the seed germination of three functional groups to low temperature and darkness in a typical steppe, Northern China

Seed germination is a key stage in the life history of plants, which has a crucial effect on plant community structure. Climate change has substantially altered the surface soil temperature and light availability, which can affect seed germination. However, whether the seed germination of different functional groups is affected by the interactions of light and temperature remains unclear. Under laboratory conditions, we examined the effects of low temperature and darkness, as well as their interaction, on the seed germination of 16 species belonging to three plant functional groups (annual and biennials, perennial grasses, and perennial forbs) in a typical steppe, Northern China. We found that low temperature had a significant negative effect on seed germination of all species. Low temperature significantly decreased the final germination percentage and germinative force of the three plant functional groups, and the germination duration of perennial grasses. Darkness significantly decreased the germinative force of perennial forbs and total seeds, and the germination duration of perennial grasses. The interactive effects of light and temperature on the seed final germination percentage and germinative force of perennial grass indicated that darkness strengthened the inhibitory effect of low temperature on the seed germination of the grass functional group. Our study indicate that the seed germination of different plant functional groups varied greatly in response to changing environmental conditions. Our results suggest that future climate change could alter the regeneration and species composition of plant communities through changing seed germination.

Comparing ameliorative effects of biomass ash and alkaline slag on an acidic Ultisol under artificial Masson pine: A field experiment

Forest soil acidification caused by acid deposition is a serious threat to the forest ecosystem. To investigate the liming effects of biomass ash (BA) and alkaline slag (AS) on the acidic topsoil and subsoil, a three-year field experiment under artificial Masson pine was conducted at Langxi, Anhui province in Southern China. The surface application of BA and AS significantly increased the soil pH, and thus decreased exchangeable acidity and active Al in the topsoil. Soil exchangeable Ca²⁺ and Mg²⁺ in topsoil were significantly increased by the surface application of BA and AS, while an increase in soil exchangeable K⁺ was only observed in BA treatments. The soil acidity and active Al in subsoil were decreased by the surface application of AS. Compared with the control, soluble monomeric and exchangeable Al in the subsoil was decreased by 38.0% and 29.4% after 3 years of AS surface application. There was a minimal effect on soluble monomeric and exchangeable Al after the application of BA. The soil exchangeable Ca²⁺ and Mg²⁺ in the subsoil increased respectively by 54% and 141% after surface application of 10 t ha^-1 AS. The decrease of soil active Al and increase of base cations in subsoil were mainly attributed to the high migration capacity of base cations in AS. In conclusion, the effect of surface application of AS was superior to BA in ameliorating soil acidity and alleviating soil Al toxicity in the subsoil of this Ultisol.