Feasibility Study on the Utilization Of Municipal Waste Fly Ash For The Manufacture Of Geopolymer Binder

Transcription

1 Feasibility Study on the Utilization Of Municipal Waste Fly Ash For The Manufacture Of Geopolymer Binder 1 Report of Activities Prepared for: Michael Rush FeNix Ash, President Prepared by: Erez N. Allouche, CEO Neil Keen, COO Carlos Montes, CTO Ruston, LA, June 15, 2015

2 2 Background: Geopolymer product encapsulation and leaching mitigation Geopolymers are cement-like materials whose crystallography consists of aluminum and silica tetrahedral structures interlinked alternately with oxygen atoms. A polymeric structure of Al-O- Si bonds is formed that serves as the main building block of the geopolymeric structure. Because of aluminum s fourfold coordination, other cations must be present in the structure in order to keep the structure neutral. This is usually done using Na +, K +, Ca 2+, and other metallic cations. These ions either play a charge balancing role, or are actively bonded into the matrix. Geopolymers have been found to exhibit better chemical and physical properties than ordinary Portland cement (OPC) for certain solidification/stabilization (S/S) applications like diminishing leachability of treated waste metals, lower permeability, improved resistance to chloride attack, and higher compressive strength. Geopolymer technology is a possible solution to some waste S/S problems. They may be used to make use of by-products or industrial wastes, and to contribute to solving environmental issues. Wastes like coal fly ash, impacted coal fly ash, incinerator ash, mine tailings, iron slag, aluminum slag, and air pollution dust (among others) can be converted into monolithic materials with low leaching levels suitable enough for construction applications with commercial value. The mechanism of trace metal immobilization in geopolymers is a combination of both chemical and physical interactions. By chemical means, the metal cation is either bonded into the matrix via an Al-O or Si-O bond, or present in the framework cavities to maintain electrical charge balance. A physically encapsulated metal cation could be substituted with another cation if its surroundings allow the diffusion process to occur. Through physical immobilization, the cation will be prevented from diffusing by one of the following processes - total encapsulation, reduced pore size, or lack of interconnected pores. The main difference with Portland cement is that it can only offer mechanical, not chemical encapsulation. Among the metals that can be encapsulated in a geopolymer matrix are Sr, Ni, Cs, Pb, Ar, Zn, Cd, Cr, Ag, Ba, Hg, Cu, Nb, Fe, Mn, Co,W, Sn, Be, and Bi. 1. Objective The objective of this research project was to evaluate the utilization of waste-to-energy (WTE) bottom ash and incinerator fly ash as a stockpile source in the manufacturing of commercial wet and dry-cast products utilizing geopolymerization technology. The study consisted of the characterization of the incinerator ash and the evaluation of eight activation systems for determining the optimal mix design formulations. Of special interest was the characterization of blends of incinerator fly ash and coal-based fly ash, in order to produce a cementitious mix with acceptable fresh and hardened properties suitable for the mass production of commercially viable products.

3 3 2. Technical considerations 1) Characterization of fly ash sample, a. Oxide composition by X-Ray Fluorescence (XRF). b. Phase composition (crystallinity) by X-Ray Diffraction (XRD). c. Loss on ignition (LOI). 2) Determination of the reactivity of the fly ash by activation with alkaline solutions. 3) Determination of the maximum utilization of the incinerator fly ash in terms of percentage by weight when blended with Class F fly ash. These blends were 100:0; 80:20; 60:40; 50:50; 40:60; and, 20:80. 4) Curing temperature of specimens: a. Oven (140 ºF for 24 hours). b. Ambient (70 ºF for 1, 3, 7 and 28 days). 5) Evaluation of the mechanical properties of the various geopolymer systems: a) Compressive strength of 2x2x2 cube specimens as per ASTM C-109. b) Compressive strength of cylindrical specimens as per ASTM C-192. c) Compressive strength of brick specimens as per ASTM C Characterization of the fly ash Table 1. Oxide Composition of Incinerator Fly Ash Oxide % Mass SiO Al 2 O MgO 1.81 Na 2 O 8.58 P 2 O SO TiO MnO BaO 0.04 Fe 2 O CaO K 2 O SrO 0.07 LOI Table 2. Phase Composition of Incinerator Fly Ash Phase Chemical Formula % Mass Calcite CaCO Thenardite NaSO Lime CaO Amorphous Content

4 4 4. Research plan The design of experiments used to manufacture the cubes is shown in Table 3. Table 3. Design of Experiments for the Feasibility Study Research variable Levels Geopolymer System 1 Geopolymer System 2 Geopolymer System 3 Geopolymer System 4 Geopolymer System 5 Geopolymer System 6 Geopolymer System 7 Geopolymer System 8 50% Coal Ash/ 10% WTE Fly Ash 40% FeNix Aggregate 50% Coal Ash 10% WTE Fly Ash 40% 3/8 and below FeNix aggregate 50% Coal Fly Ash 10% WTE Fly Ash 40% 3 and below FeNix aggregate Wet-cast cylinders 50% Coal Ash/ 10% WTE Fly Ash 40% FeNix Aggregate Ambient cure (70 ºF) 50% Coal Ash 10% WTE Fly Ash 40% 3/8 and below FeNix aggregate Ambient cure (70 ºF) 50% Coal Fly Ash 10% WTE Fly Ash 40% 3 and below FeNix aggregate Ambient cure (70 ºF) 40% Coal Ash/ 10% WTE Fly Ash 40% FeNix Aggregate Dry Cast Bricks 50% Coal Ash 10% WTE Fly Ash 40% 1/4 and below FeNix aggregate Dry Cast Bricks

5 5 5. Cube specimen preparation and compressive strength results Cube specimens for all geopolymer systems were mixed and cast according to ASTM C-109. The formulations of these systems along with an AGS control are shown in Table 4. Compressive strength results are shown in Table 5 and Figure 1. Table 4. Weight Percentages and Ratios of the Components of the Mix. System (wt.%) Component Aggregate FeNix WTE Ash Coal Fly Ash C Ash FeNix Sand FeNix 3/8 & below FeNix 3 and below Sand Activator Solution Water Table 5. Compressive strength results for all geopolymer systems at 1, 3, 7 and 28 days. 1 day (psi) Sample AGS ,950 3,409 3,586 3, ,057 1,925 2, ,010 3,455 3,710 3, ,095 2,024 2, ,986 3,350 3,576 3, ,115 1,196 1,905 2,283 Avg. 5,982 3,404 3,624 3, ,022 1,116 1,951 2,290 St. Dv day (psi) Sample AGS ,985 4,870 5,124 5,680 1,726 1,934 2,115 2,750 3, ,954 4,798 5,153 5,532 1,735 1,930 2,148 2,810 3, ,015 4,856 5,183 5,589 1,703 2,037 2,215 2,756 3,310 Avg. 7,984 4,841 5,153 5,600 1,721 1,967 2,159 2,772 3,258 St. Dv day (psi) Sample AGS ,865 4,863 5,123 5,540 2,655 2,975 3,255 2,756 3, ,924 4,775 5,214 5,512 2,670 2,839 3,159 2,764 3, ,970 4,810 5,174 5,544 2,621 2,910 3,164 2,870 3,258 Avg. 7,919 4,816 5,170 5,532 2,648 2,908 3,192 2,796 3,210 St. Dv day (psi) Sample AGS ,014 4,870 5,124 5,680 3,794 4,250 4,650 2,841 3, ,932 4,798 5,153 5,532 3,815 4,175 4,647 2,749 3, ,983 4,856 5,183 5,589 3,745 4,218 4,586 2,789 3,215 Avg. 7,976 4,841 5,153 5,600 3,784 4,214 4,627 2,793 3,209 St. Dv

6 6 Figure 1. Compressive Strength of all Geopolymer Systems at 1, 3, 7 and 28 Days. 6. Manufacture of geopolymer bricks Two batches, containing 12 bricks per batch, were prepared using an automatic brick making machine for geopolymer systems 7 and 8. Figure 2. Manufacturing of Geopolymer Bricks.

7 7 This procedure demonstrated the suitability of the proposed mix designs to be manufactured on mass scale using a commercial, automated dry-cast bricks making machines. This ability is a key element in enabling the conversion of tens-of-thousands of tons of incinerator ash into beneficial products in a cost effective manner. 4 x4 x2 brick samples were prepared from the dry-cast brick and tested for compressive strength following the clauses of ASTM C1314. The results are summarized in Table 5 and are shown graphically in Figure Additional testing Due to the unique and interesting nature of the materials provided by FeNix, and our interest in those materials, we have expanded the material feasibility testing programs to include limited product feasibility testing. The materials provided have characteristics that are favorable for a wide variety of commercial applications, and their availability and low cost add to their viability to be utilized in large volumes. We feel that FeNix s materials are candidates for use in products such as burial vaults, septic tanks, floor tiles, industrial countertops, headstones, veneer stone, bricks, outdoor furniture, walkway pavers, soil retention blocks, residential and commercial building systems, insulated concrete form fill, fire-proofing and many other products. Figure 3 below displays images of selected products manufactured using FeNix s fly ash and aggregates. Figure 3. Construction and Landscape Products Manufactured from FeNix s Bottom ash and fly Ash waste streams.

8 8 8. Discussion A comprehensive testing program was undertaken to explore the ability of FeNix s bottom ash and fly ash streams, by-products of the incineration of side-curb municipal waste, to be used as a stockpile in the manufacturing of cementitious-based products for construction, landscaping and other industries. Eight geopolymer formulations were developed covering a range of casting and curing practices. The geopolymer-based incinerator concrete was found to exhibit a compressive strength, a key measure of quality in the concrete industry, of up to 5,500 psi in as little as three (3) days, performance that meets or exceeds most commercially available Portland-cement formulations of concrete products. One market segment that was identified as an initial target area for incinerator ash-based geopolymer concrete is the dry-cast manufacturing of semi-structural pre-cast products. These products, used in large quantities in the housing, infrastructure and landscaping industries, can be sold via wholesale and retail vendors and are not subjected to the same level of specifications and testing commonly required by public agencies. Furthermore, dry-cast manufacturing minimizes the quantity of activator solution needed, thus enhancing the cost effectiveness of these products, which adds appeal to their exceptional green nature. The dry-cast geopolymer specimens reached or exceeded a compressive strength of 3,000 psi in 28 days, which is three times the minimum value specified by the relevant ASTM standard (ASTM C 140), of 1000 psi in 28 days. The one-day strength of 2,000 psi could easily support the handling procedures required for turning the molds, and likely can support as many as three production cycles per day. Ambient cure geopolyer systems exhibited a 28-day compressive strength as high at 4,600 psi, nearly matching the performance of the oven-cured specimens, although the strength gain rate was slower. This is indicative of the similar level of geopolymerization that was achieved at the end of the 28-day test period. Ambient cured, wet-cast geopolymer systems are suitable primarily for cast-in-place field applications. The concept of taking the largest solid-waste stream on the planet, and converting it to usable energy, recycled metals and construction products, with no residual left over is an extremely powerful concept from a sustainability prospective, as well as from a business prospective. The planet population is projected to exceed 8 billion by 2030, with 63% of the population living in urban areas, phenomena that together with the rapid development of a large middle-class in Asia, results in the production of 2.8 billion metric tons of solid waste from all sources each year, or approximately 2.2 lb per capita per day. This value is expected to increase by as much as 8% per year over the next decade. To put it in prospective, the total volume of solid waste expected to be generated over the next 100 years is approaching to the mass of Mount Everest (approximately 6,400 Billion matrix tons). The combination of waste-to-energy and metal extraction processes, with the conversion of the resulting incinerated bottom ash and fly ash to construction products presents a path to a sustainable global urban society, as well as one of the most promising economic opportunities associated with the rapid urbanization of our planet.