Stabilization of biomass ash granules using accelerated carbonation to optimize the preparation of soil improvers

[Display omitted] •Better pH adjustment of materials was reached using moist granules and CO2 dry gas.•Accelerated carbonation reduces stabilization time from 1-year to 20–80 h.•AFR allows a similar carbonation rate to HPR in lesser reaction times.•Plant nutrients’ leachability (B, Mg, Mn, Mo and P) was enhanced in accelerated mode.•Minimum CS was reached in accelerated mode to ensure materials’ physical stability. After the revision of the Fertilizer Regulation (EC 2019/1009), biomass ash can be used as component material for soil improvers to be placed on the EU market. This provides opportunities for large scale recycling of biomass ash. However, this material cannot be directly applied to soil without stabilization by carbonation, which also creates an opportunity for CO2 capture and storage. Here, accelerated carbonation in an atmospheric fixed-bed reactor (AFR) was applied to prepare ash granules (AG). Relative humidity of gas, temperature, reaction time and CO2 concentration were optimized and further tested in a closed high-pressure reactor (HPR). Materials resulting from both reactors were compared with those obtained after 1-year of carbonation under atmospheric conditions. This study showed that AFR accelerated tests resulted in a significant reduction of the reaction time than HPR to achieve a similar pH adjustment. Also, under 100 vol.% CO2 atmospheric conditions, pH and electrical conductivity reached target values faster than under 15 vol.% CO2 conditions. Based on results obtained here we recommend AFR operating at 25 °C and 100 vol.% CO2 for 20 h, as the optimal procedure for stabilization of AG. In this study we provide evidence that accelerated carbonation enables a much faster and cost-efficient preparation of potentially valuable soil additives than natural carbonation. Also, leaching tests revealed that plant nutrient availability (B, Mg, Mn, Mo and P) was increased under accelerated carbonation compared to natural carbonation. The present work paves the way towards the development of optimized protocols to effectively recycle biomass ashes for soil recovery.