Geotechnical Properties and Application of Lime Modified Phosphogypsum Waste

Advances in Civil Engineering

Okonta

Ntuli

2018

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The use of industrial waste as a potential stabilizer of marginal construction materials is cost effective. Phosphogypsum and fly ash are industrial wastes generated in very large quantities and readily available in South Africa. In order to explore the potential stabilization of vastly abundant expansive soil using larger quantity phosphogypsum waste as a potential modifier, composites with a mixture of lime-fly ash-phosphogypsum-basic oxygen furnace slag were developed. However because of the presence of radionuclide, it was necessary to treat the phosphogypsum waste with mild citric acid. The effect of the acid treatment on the geotechnical properties and microstructure of expansive soil stabilized with phosphogypsum-lime-fly ash-basic oxygen furnace slag (PG-LFA-BOF) paste was evaluated, in comparison with the untreated phosphogypsum. Expansive soil stabilized with acid-treated PG-LFA-BOF paste exhibited better geotechnical properties; in particular, the high strength mobilized was associated primarily with the formation of various calcium magnesium silicide and coating by calcium silicate hydrate and calcium aluminate hydrate. The soil microstructure was improved due to the formation of hydration products. The stabilized expansive soil met the specification for road subgrades and subbase. Stabilization of expansive soils with phosphogypsum, fly ash, and basic oxygen fly ash does not only improve engineering properties of soil but also provides a solution in relation to disposal and environmental pollution challenges.

Section: Curing Determination Of Unconfined Compressivementioning

confidence: 99%

Geotechnical Properties and Microstructure of Lime‐Fly Ash‐Phosphogypsum‐Stabilized Soil

Advances in Civil Engineering

Okonta

Ntuli

2018

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“…The product was intact and the highest strength of 3.52 MPa is applicable for load bearing applications. In terms of UCS and durability, the developed geopolymer has equivalent strength values as C1-C4 materials, which is applicable for subbase [56]. The product also meets the requirements of South African Roads specification.…”

Section: Image Of Geopolymer Developedmentioning

confidence: 96%

Recovery of Silicon Dioxide from Waste Foundry Sand and Alkaline Activation of Desilicated Foundry Sand

Sithole

2020

J. Sustain. Metall.

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This study was conducted to recover silica (desilication) as a valuable metalloid from waste foundry sand (WFS) by a leaching process and to find application for desilicated foundry sand (DFS). The leaching time applied was 5 h; 3 M of potassium hydroxide (KOH) was used as a leaching reagent. The agitation speed of 200 rpm and the liquid/solid ratio of 25 were found to be the best conditions for optimum leaching results. A geopolymer from DFS was developed by using NaOH as an alkaline activator. The results obtained showed that the optimum conditions for the synthesis of a geopolymer were 15 M NaOH, 150 µm DFS particle size, and a curing temperature of 80 ℃ for 72 h. The geopolymer strength development was due to the formation of Phillipsite and Kalsilite as new hydration products. At the optimum alkaline solution concentration, the highest unconfined compressive strength (UCS) of 4.8 MPa was achieved. The developed geopolymer met the minimum strength requirements for load bearing material. This study provides an innovative and novel solution for the beneficiation of spent foundry sand and the recovery of a valuable metalloid, resulting to zero waste generation. Graphical Abstract

“…Water absorption in % by weight = (Wf -Wi)/Wi x 100 (2) It is preferred that specimen absorb as less water as possible (24 hr absorption process) in order for them to give high durability results. After observing that the highest unconfined compressive strength was obtained at 80 o C, it was then decided that specimen that will undergo inundation tests be oven dried at the same temperature (80 o C) for five days.…”

Section: Water Absorption Of the Produced Specimen For Raw And Treatementioning

confidence: 99%

“…South Africa has a highly developed domestic and export oriented phosphate industry, with the largest igneous phosphates deposits located in Phalaborwa in the northern province of the country [1]. Residual deposits of Phosphogypsum are readily available in large quantities in South Africa and currently are landfilled or pumped into the sea [2]. Waste Phosphogypsum is produced as a by-product during the treatment of phosphate concentrates with sulphuric acid to produce phosphoric acid according to the following simplified chemical reaction [3].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of raw and chemically treated waste phosphogypsum and its potential applications

2019

E3S Web Conf.

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A million tons of Phosphogypsum (PG) is stacked in the environment every year and is progressively considered an asset. South African construction industry is expanding as a result of infrastructural developments in the country, the reuse of PG in this industry is considered for recycling and reducing the stacks in landfills. Phosphogypsum is known for its limited ability to use in cement industry due to its phosphorus and radionuclides impurities. This study was conducted to reduce these impurities and investigate the probability of PG application in building and construction. Leaching of PG with citric acid was conducted whereby a relative proportion of P 2 O 5 and radionuclides was reduced in the material, constituents which contributes to strengths reduction. Optimum moisture Contents and maximum dry densities were determined for various PG content mix designs in which Lime and Fly Ash were added to stabilise PG material. The composites were compacted at various moisture contents and cured at low and elevated temperatures of at 40 o C and 80 o C for 4 days. The results obtained shows that for unconfined compressive strengths; the composites produced from PG, and cured at high temperature qualified for the use in construction industry. , 0 (201 Web of Conferences https://doi.org/10.