2212-6708 © 2014 Richa Sehgal. Published by Elsevier B.V.Selection and peer review under responsibility of Asia-Pacifi c Chemical, Biological & Environmental Engineering Societydoi: 10.1016/j.apcbee.2014.01.016

APCBEE Procedia 9 ( 2014 ) 87 – 91

Available online at www.sciencedirect.com

ScienceDirect

Carbon Dioxide Sequestration in Alkaline Top Soil Using Alkaline wastes

Richa Sehgala,*, Luv Sehgalb, Arvind Kumar Nemac and Prakhar Guptad

aDepartment of Civil Engineering, Indian Institute of Technology Delhi, New Delhi-110016, India bEngineer Trainee, WAPCOS Ltd. (Govt of India Undertaking-Ministry of Water Resources), Jaipur-302016, India

cDepartment of Civil Engineering, Faculty Environmental Engineering, Indian Institute of Technology Delhi, New Delhi-110016, India dDepartment of Civil Engineering, Indian Institute of Technology Delhi, New Delhi-110016, India

Abstract

Due to growing concern about climate change and global warming, new ways must be developed to reduce CO2 emissions in atmosphere. Incinerator ash produced in municipal treatment facilities and marble-dust produced during marble cutting process are alkaline wastes. This paper examines the carbon mineral sequestration potential of mixing alkaline wastes in two soil samples in accelerated carbonation conditions. Six different percentages of alkaline wastes in 20g sample were used. Batch reactor conditions were maintained at 40°C, relative humidity 60-70% and CO2 flow-rate of 10 litres-a-minute. Optimum water content was found by carrying out experiments on a sample with 7 different water-to-solid ratio (0, 0.2, 0.4, 0.6, 0.8, 1 and 1.2).The particle-size effect was gauged by taking soil samples sieved through standard sieve sizes of BSS25 and BSS50. It was concluded that low water-to-solids ratio is better for carbonation, although some minimum amount of water is necessary for reaction. The optimum water-to-solids ratio for incinerator ash comes to be 0.4. Marble dust was found to be inefficient to capture CO2 due to lower pH and due to lump formation. As expected, carbonation was higher for samples with less particle size and higher surface area. © 2013 Published by Elsevier B.V. Selection and/or peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Keywords: Alkaline waste, incinerator ash, marble dust, mineral sequestration

1. Introduction

* Corresponding author. Tel.: +917838920515 E-mail address: richasehgal2908@gmail.com.

2013 5th International Conference on Chemical, Biological and Environmental Engineering(ICBEE 2013)

2013 2nd International Conference on Civil Engineering (ICCEN 2013)

© 2014 Richa Sehgal. Published by Elsevier B.V.Selection and peer review under responsibility of Asia-Pacifi c Chemical, Biological & Environmental Engineering Society

88 Richa Sehgal et al. / APCBEE Procedia 9 ( 2014 ) 87 – 91

Due to increased awareness of the threats posed by climate change and global warming, a lot of methods are being investigated to reduce the anthropogenic carbon dioxide emissions. The need for carbon dioxide removal has been expressed by many individuals and organizations worldwide [1].

Efforts to capture and store carbon dioxide have so far focused on sequestration in natural reservoirs such as oceans, geological rock formations and terrestrial biosphere [2]. We use the fact that carbon dioxide is anhydrous oxide of carbonic acid. Alkaline wastes neutralize this acid to carbonates and bicarbonates. These products tend to be chemically stable. Rock minerals can be used to sequester CO2 but using alkaline wastes has various advantages over the use of rock minerals, as the process can be expected to be faster owing to the relatively open structure and higher specific surface area of the wastes [3].

Incineration involves the combustion of organic materials contained in waste. The amount of ash produced by the municipal solid waste incinerators varies from 5 to 10 per cent by volume of the original quantity of waste [4]. The ash residue remaining after combustion has been shown to be a non-hazardous solid waste which has been tested for ecotoxic metals[5].The ash is alkaline in nature and has the potential to capture atmospheric carbon dioxide.[6] Marble is a metamorphic rock and has been used as a construction material for ages. Marble pieces need to be cut into smaller blocks to give them the desired shape. During this process about 25 per cent of the original marble is lost in the form of marble dust [7].

This project aims at to estimate the sequestration potential of alkaline wastes in soil. The two alkaline wastes used are incinerator ash and marble dust. Higher surface area, fine grained, readily available, generated at point source and rich source of calcium and magnesium are few properties which make them a potential source for sequestration. Also, with the utilization of wastes, problem of their disposal is also taken care of.

2. Materials and Methods

Experiments were conducted on different mixtures of alkaline wastes with soil. Incinerator ash was collected from OKHLA plant of the Delhi Municipal Corporation and marble dust (Makrana) was collected from Rajouri Garden, Delhi. The top soil samples were collected from two sites in I.I.T Delhi to obtain soil(A) and soil(B). In the first part of the experiment the optimum water content was evaluated. The second part deals with the effect of particle size on sequestration potential.

2.1. Sample Preparation

The soil samples, incinerator ash and marble dust were grinded to obtain homogenous system. The 2 types of soil samples were sieved through sieves BSS25 (0.6mm) and BSS50 (0.3mm), i.e. 1:2 ratio of sieve size. The samples were oven dried at 100°C to ensure there is no initial moisture content. For each of the four soil types and two types of alkaline wastes, six different percentages of alkaline wastes in 20g of sample are used (0, 20%, 40%, 60%, 80%, 100%) giving us 48 samples. In the 20g sample, 8g distilled water was added according to the optimum water content (0.4 in this case). The mixtures were manually mixed. Each type was prepared in duplication, to obtain the hydroxide content before and after carbonation.

2.2. Carbonation chamber

The carbonation chamber used in Fig. 1 was used. It is a rectangular chamber with a working volume of 393 litres [8]. The upper half of front face of the reactor was fixed. The CO2 entered through 2 valves fitted on the right side of the reactor wall. A rotameter was fitted in the path of gas flow to maintain the CO2 flow rate. A digital thermostat was used to maintain temperature at 40°C. A trough containing water was placed to maintain humidity. It had four fans on reactor walls to ensure circulation in the whole reactor [9].

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2.3. Carbonation reaction

All the samples were kept in the chamber. The chamber was then closed. CO2 was allowed to flow for 2 hours. The reaction was allowed to continue for at least 16 hours.

2.4. Experimentation

All the samples before and after carbonation were subjected to experimentation. The difference in hydroxide alkalinity in samples before carbonation and after carbonation was calculated to estimate the carbonation potential. 10 g of sample was taken in a conical flask. 100 ml of distilled water was added to it. The flask was kept on a magnetic stirrer and stirred for 5 minutes, with heating. After this, samples were kept to settle for 24 hours without disturbance. Samples were filtered using filter papers and 50 ml of each filtrate was taken and tested with a pH meter. The following formula is used to determine the hydroxide alkalinity:

[OH-] = {10 ^ (pH-14)} * 50000 (carbonates mg / litre)

Fig. 1. Carbonation chamber line diagram

Accelerated carbonation technique was used to have results in short period of time. Soil samples were exposed to CO2 at 10L/min rate which is much more than normal atmospheric condition. Icing of CO2 cylinder valve was a major problem faced during experiments, which was resolved by using external Heater.

3. Results and Conclusions

This paper demonstrates the evaluation of CO2 sequestration in alkaline top soils using two different alkaline wastes. Samples in the carbon reactor were exposed to constant CO2 flow rate under standardized humidity, temperature conditions and varying proportion of alkaline waste.

As can be seen from Fig. 2, the maximum carbonation occurs in case of water-to-solids ratio of 0.4. Also, we can see that the carbonation in case of no water is negligible, showing that some minimum amount of water is necessary for reaction to take place. And carbonation is low for high water content. It indicates that more water leads to hindrance in CO2 diffusion and hence low accessibility for reaction. Thus, Carbon dioxide cannot diffuse properly to reach sites for carbonation.

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Table 1. Using (8g ash + 12g soil) with varying water-to-solids ratio

Ratio of water-to-solids Before carbonation After carbonation Hydroxides consumed

(mg/l) pH [OH-] (mg/l)

pH [OH-] (mg/l)

0.00 10.53 16.94221 10.51 16.17968 0.762525 0.20 10.53 16.94221 8.12 0.065913 16.87629 0.40 10.56 18.1539 8.25 0.088914 18.06499 0.60 10.53 16.94221 8.7 0.250594 16.69161 0.80 10.55 17.74067 9.35 1.119361 16.62131 1.00 10.54 17.33684 9.23 0.849122 16.48772 1.20 10.55 17.74067 10.2 7.924466 9.816204

Fig. 2. Optimum water content observations

The common feature in all the graphs is that the amount of hydroxides consumed is higher for samples sieved through BSS50 (i.e. 0.3mm) than that for BSS25 (i.e. 0.6mm). It indicates that smaller the particle size, higher is the surface area available, and thus, more is carbonation in the sample. We can see from Fig.3 that for incinerator ash, the results are as expected. The carbonation extent increases with increasing ash content.

Fig. 3. Observations for incinerator ash

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Also, seen in Fig. 4, in the case of (Marble dust + soil (B)), the carbonation increases in the beginning and then decreases. The increase in the beginning is due to higher pH of dust compared to soil (B). According to our inference, lump formation in marble dust during experiments diminished its carbonation capacity. The surface area available for carbonation decreases with lump formation. Thus, as marble dust content increased, less carbonation occurred. This was confirmed by results in the case of (Marble dust + soil (A)). Soil (A) and marble dust had almost same initial pH, and thus, carbonation decreased with increasing marble dust content.

Fig. 4. Observations for marble dust

The results presented in the project indicate that Incinerator ash could be used to sequester the CO2 emissions. The marble dust was found to be inefficient to capture CO2. The most important future application of such emerging technology will be utilization of such alkaline waste material as cover for barren land with some amount of water, to make use of the otherwise waste land to help in carbon dioxide sequestration.

References

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[2] W.J.J. Huijgen, and R.N.J. Comans, “Carbon Dioxide Sequestration by Mineral Carbonation Literature Review, Energy Resource Center of the Netherlands”, ECNC-03-016, 2003.retrieved on 29.12.2010.

[3] Deborah N. Huntzinger, John S. Gierke, S. Komar Kawatra, Timothy C. Eisele, and Lawrence L. Sutter “Carbon Dioxide Sequestration in Cement Kiln Dust through Mineral Carbonation” Publication Date (Web): 05 February 2009

[4] U.S. Environment Protection Agency, “Wastes-Non Hazardous Waste-Municipal Solid Waste” Last updated on 7/24/2012 [5] Abbott, John; Coleman, Peter; Howlett, Lucy; Wheeler, Pat "Environmental and Health Risks Associated with the Use of

Processed Incinerator Bottom Ash in Road Construction". AEAT/ENV/R/0716 (October 2003)., BREWEB [6] Jianguo Jiang, Sicong Tian, Chang Zhang, “Influence of SO2 in incineration flue gas on the sequestration of CO2 by municipal

solid waste incinerator fly ash”, Journal of Environmental Sciences, Vol. 25 No. 4 , ISSN 1001–0742, (2013) [7] Bahar Demirel. “The effect of the using waste marble dust as fine sand on the mechanical properties of the concrete”.

International Journal of the Physical Sciences Vol. 5(9), pp. 1372-1380, 18 August, 2010 [8] G.Anjali, M.Bhavya, and N.Arvind Kumar, “CO2 Sequestration Potential of Construction and Demolition Alkaline Waste

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