Evaluation of industrial wastes as sources of fertilizer silicon using chemical extractions and plant uptake

Abstract

Six inorganic industrial‐waste materials (coal fly ash, bauxite‐processing mud, steel slag, two samples of air‐cooled blast furnace [BF] slag, and one sample of water‐cooled BF slag), along with wollastonite, were evaluated as fertilizer‐Si sources. Evaluation was carried out by analyzing total and extractable Si fractions in the materials, by incubating them at two rates with a Si‐deficient soil and measuring potentially available extractable Si and by measuring yield and Si uptake by two successive rice crops grown in the fertilized soils. Of the waste materials used, fly ash had the highest total Si content (29%) but a negligible quantity was present in extractable forms. Steel slag and bauxite‐processing mud had only 5%–7% Si content while BF slags contained 14%–18% Si. All materials, other than fly ash, increased the amount of extractable Si present in the soil. Additions of steel slag and bauxite‐processing mud caused greater increases in Si extractability than the air‐cooled BF slags while water‐cooled BF slag–treated soils contained notably high acid‐extractable Si. Because of the alkaline nature of the materials, and their reaction products, there was a positive relationship between extractable soil Si and soil pH. However, an equilibration experiment using NaSiO3 as the Si source confirmed that Si solubility in the soil decreased with increasing pH. Dry‐matter yields of rice, at the lower rate of Si addition, were increased by all treatments other than fly ash. The higher rates of steel slag and bauxite‐processing mud caused yield depressions. Total Si uptake by rice was increased by all treatments, other than fly ash, and was greater at the higher rate of Si addition. It was concluded that the BF slags are the most effective waste materials as fertilizer‐Si sources and that, in slag‐amended soils, CaCl2 and NH4 acetate are the most reliable soil‐test extractants.

Silicon Sources for Agriculture

“…) and red mud (1.093 mg L −1 ) was well below the regulatory limit of 5.0 mg L −1 and TCLP-Pb in red mud (0.016 mg L −1 ) was also low (Haynes et al 2013). Compared to the maximum allowable limits (MALs) for Cr (4 %) set up in Japan (Ma and Takahashi 2002), the total Cr content of all these slags (Table 12.2) is far below the MAL.…”

Analysis of Silicon in Soil, Plant and Fertilizer

“…Given in Table 2.10 are quantities of total and extractable Si in the waste materials tested (Haynes et al 2013 ). The data listed in Table 2.10 clearly indicate that the total Si was over 20 % in fl y ash and Ca silicate and between 14 % and 18 % in the BF slags, while it ranged from 5.4 % in the steel slag to 6.8 % in the processing mud.…”

Silicon Release from Local Materials in Indonesia under Submerged Condition

“…Fly ash is made up of highly insoluble, glass-like particles, consisting of amorphous ferro-aluminosilicate and quartz (Haynes et al, 2013). The total amount of Si released from fly ash was higher in red clayey soil, which was due to lower pH in soil solution (Table 3).…”

“…Fly ash from coal combustion where the dust-collection system removes the fly ash from the combustion gases before they are discharged in the atmosphere is high in Si content (Ramezanianpour, 2014). These Si rich materials from industrial wastes are also applied to increase soil pH (Haynes et al, 2013).…”