Use of Vietnamese rice husk ash for the production of sodium silicate as the activator for alkali-activated binders

TLDR: In this article, a low cost, low environmental impact sodium silicate solution (waterglass) from Rice Husk Ash (RHA) and more specifically RHA from Vietnam was developed.

About: This article is published in Journal of Cleaner Production.The article was published on 2018-11-10 and is currently open access. It has received 121 citations till now. The article focuses on the topics: Fly ash & Geopolymer.

Figures

Table 7 Cost comparison for the activation of 1 m3 of AAC

Figure 6 Effect of (a) heating temperature and (b) heating time on the yield of silica and mortar compressive strength. Obtained results seemed to indicate that the optimal process parameters for the production of RHA - derived sodium silicate solution were: concentration of NaOH solution of about 3 M and heating temperature of 80 °C for 3 hours. A marked reduction in the NaOH content of the dissolving solution was achieved when compared to available literature (Bouzón et al., 2014, Tchakouté et al., 2016a), with obvious positive impacts on economic and environmental performances.

Figure 11 XRD pattern for pastes activated with RHA-derived and commercial alkaline solutions at (a) 7 days and (b) 28 days.

Figure 1 Comparison between (a) close vessel process for sodium silicate; (b) proposed method for the production of RHA-based sodium silicate solution.

Figure 12. FTIR spectra for unreacted FA, GGBS and pastes activated with RHA-derived and commercial alkaline solutions at (a) 7 days and (b) 28 days.

Figure 4 XRD patterns of RHA, FA and GGBS

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Use of vietnamese rice husk ash for the production of sodium silicate as the activator for alkali-activated binders" ?

This research investigated the production of a low cost, low environmental impact sodium silicate solution ( waterglass ) from Rice Husk Ash ( RHA ) and more specifically RHA from Vietnam. Sodium hydroxide solution concentration, process temperature and duration were studied. Results from a simplified preliminary environmental analysis suggested increased sustainability of the RHA-derived solution when compared with commercially available waterglass. 

Q2. What were the main factors affecting the dissolution of silicates from RHA?

Heating duration and temperature, and NaOH concentration were investigated as main factors affecting the silicate dissolution from RHA. 

Q3. Why did the first peak develop after about 1 hour?

The second peak, developed between 80 and 90 minutes for samples prepared with waterglass, is probably due to the formation of calcium silicate hydrate gel, which is promoted by the availability of free Si species in the activating solution. 

Q4. What was the mass loss calculated between 200 and 600 °C?

The mass loss calculated between 200 and 600 °C was 3.06% and 3.25% for samples activated withcommercial and RHA-derived solutions respectively, whilst it was 2.22% for the sample activated with NaOH only. 

Q5. How much electricity would be produced from rice husk?

If all the rice husk was used for electricity generation, it would produce approximately 8.7 billion kWh of electricity and 1.7 million tonnes of rice husk ash (RHA) per year. 

Q6. What are the advantages of alkali activated binders?

In order to reduce the CO2 emissions, geopolymers or alkali-activated binders (AAB) are considered to offer an alternative to PC for concrete production. 

Q7. How much energy is required to keep the temperature of the vessel?

The efficiency of the insulation system in maintaining the required temperature of the vessel over the time was assumed to be 30% (i.e., some energy is required to keep the temperature for 3 hours as the insulation of the hypothetical vessel is not perfect). 

Q8. What is the reason why the microstructural analysis was carried out only on samples prepared with R?

the microstructural analysis was carried out only on samples produced with RHA with a low amorphous content, whereas the strength reduction was also observed on samples prepared with almost fullyamorphous RHA. 

Q9. What is the effect of the pH value of the solution on the dissolution rate of silic?

The reduction of the final compressive strength of mortar samples when NaOH concentration was lower than 2 M indicates that the pH value of these solutions may entail changes in the degree of polymerisation of the dissolved chemical species (Torres-Carrasco and Puertas, 2015). 

Q10. How was the energy used for the production of sodium silicate?

RHA from Vietnam, obtained through an incineration process with controlled temperature and duration that produced an almost fully amorphous material, was investigated as silicate source for the production of alternative sodium silicate solution. 

Q11. What is the energy used for the production of electricity in a boiler?

The energy obtained from the combustion of rice husk could in theory be used for production of electricity in a boiler, and indeed this would be the preferred option, provided it is technically feasible. 

Q12. What was the average particle size of the RHA?

Average particle sizes (d50) were 16.8 and 14.4 µm for FA and GGBS respectively, whilst particle densities were 2.42 and 2.92 g/cm3 for FA and GGBS respectively. 

Q13. What is the effect of the use of waste-derived activators on the environment?

The use of waste-derived activators can mitigate both of these problems, provided that such alternative activators show the same efficiency as commercially available chemicals. 

Q14. What are the costs associated with the production of the RHA-derived waterglass?

Costs associated with the production of the RHA-derived waterglass are mainly: (a) the cost of RHA, (b) the cost of NaOH, (c) the cost of energy for heating the solution up to the process temperature (i.e., 80 ℃) over the process duration (i.e., 3 hours). 

Q15. What was the IC used to determine the initial and final setting time of mortar mixes?

The initial and final setting time of mortar mixes were determined by probe penetration resistance according to ASTM standard C403M-08.A TAM 

Q16. What were the values of EE and CF for the RHA-based waterglass?

Values of EE and CF for the RHA-based waterglass were estimated by consideringthe environmental impacts of rice husk combustion, production of the NaOH used in the solution and the solution heating process. 

Q17. Why was the energy contribution from rice husk combustion not included in the analysis?

due to the uncertainties related to this, the energy contribution from rice husk combustion was not included in the analysis.