BACKGROUND The biomass‐fired power in China is mainly fueled by agro‐residue, and is suffering the bottlenecks of feedstock supply, super heater corrosion and nutrient cycle. How to recycle the ash nutrient to farmland is crucial for ecological sustainability. This work investigated potassium recovery from the fly ash of a grate boiler firing agro‐residue using leaching methods. RESULTS The studied ash contains a massive amount of fixed carbon (158.92 mg g−1) and little volatile matter (39.44 mg g−1). The unburnt carbon strongly decreases the concentration (CK) in the leachate and recovery percentage (RPK) of potassium nutrient by 17.6–24.1% and 9.0–18.8%, respectively. Calcination pretreatment in air at 500 °C for 30 min should be employed before leaching to remove the unburnt carbon. Mineralogy analysis shows that low‐temperature pre‐calcination (≤575 °C) does not affect potassium solubility. Under the optimal leaching of calcined ash in water with liquid‐to‐solid ratio 3 for 30 min at room temperature, CK in the leachate, dissolution percentage (DPK) and recovery percentage (RPK) of potassium element reached 17.21 g L−1, 82.0%, and 62.6%, respectively. CONCLUSIONS The fly ash from grate boilers firing agro‐residue is much better than other marginal potash sources. This work is helpful to improve the technology of agro‐residue fired power. © 2016 Society of Chemical Industry

The self-adaptive vegetation concrete is a porous concrete which has characteristics of self-adaptation (suitable for acid-alkali degree and humidity that plant grow automatically), self-supply (the necessary nutrition element offers plants to grow within the structure) and necessary mechanics of the project. To meet the vegetable growth in self-adaptive vegetable concrete, the base body of vegebable concrete is produced with many kinds of cementitious material and complex of different aggregate. The experiment shows that the vegetable concrete base body which has a suitable acid-alkali degree environment of seed sprout (PH < 9) and suitable space environment for plant root system growth( porosity rate > 40%) is produced through using self-made soil stabilizer (the proportion of soil stabilizer and the clay is 1:1) and different aggregates (cobble, coral reef and ceramsite).

In order to find the proper calcination temperature of gangue, gangue samples calcined at different temperatures were examined by X-ray diffraction (XRD), infrared spectroscopy (IR) and magnetic angle spinning nuclear magnetic resonance (MAS NMR). It was found that the structure of kaolinite in the gangue sample was destroyed and the relative content of illite crystal in the sample increased when the sample was calcined up to 500°C. The XRD peaks of illite disappeared in the gangue sample calcined at 700°C. The XRD spectra showed the formation of mullite at about 1000°C. With the increase of the calcination temperature, the octahedral (6-coordinated) aluminum was transformed to the tetrahedral (4-coordinated) aluminum gradually. For gangue sample calcined at 700°C, the 29 Si MAS NMR sharp peak of Q 4 was left. Compared with kaolinite in gangue, the thermal transformed temperature of pure kaolinite was lagged. To obtain metakaolinite, the optimum calcination temperature of this gangue was about 500°C.

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