Elsevier

Journal of Cleaner Production

Volume 204, 10 December 2018, Pages 1097-1107
Journal of Cleaner Production

New possibilities of neutralisation sludge solidification technology

https://doi.org/10.1016/j.jclepro.2018.08.095Get rights and content

Abstract

This paper presents the procedure and results of research on the effectiveness of metal immobilisation in treated neutralisation sludge with the help of the solidification method using cement and power plant filter fly ash. Qualitative and quantitative tests were performed to assess the suitability of the developed materials – solidification products. The studied solidification technology will allow the use of the solidification products as a filler material for recultivation works in landfills, as a buffer layer or underlying layer during the construction of roads or in subfloors, and for installation of technological units in landfills.

Introduction

Due to the continuous production of neutralisation sludge in industrial production, in addition to the amount of this sludge occurring at sites with old ecological burdens of up to tens of thousands of tons, we expect that there will be a continuing need to address the way that this waste is handled in accordance with a valid hierarchy of waste disposal in the European Union (EU) (Directive 2008/98/EC, 2008) in ways other than landfill. Furthermore, in connection with the ongoing and planned redevelopment of old ecological burdens, especially in cases where neutralisation sludge was deposited on the surface of the terrain without proper hydrogeological and technical protection, the solidification/stabilisation (S/S) treatment of this sludge, using the proven formula, results in significant cost savings. Above all, waste management within the EU must be directed at not only reducing the amount of waste produced, but also eliminating its hazardous properties, which can have a negative impact on the environment and the health of the population, and reducing landfill waste.

The use of waste as a raw material can be very beneficial from an environmental point of view. On the one hand, there is no unnecessary consumption of raw materials, while on the other hand, waste is being used that would otherwise be deposited in a landfill and unnecessarily pollute the environment. The problem, however, is how to evaluate the materials generated by the treatment of waste. In the case of product reprocessing, it is necessary to follow the product-related regulations. In the case of a construction product, the assessment must be in accordance with Regulation No 305/2011 of the European Parliament and the Council of EU from 9 March 2011, setting out harmonised conditions for the marketing of construction products, which repeals the Council Directive 89/106/EHS (Regulation (EU) No 305/2011, 2011). However, in most cases, the basic product law and its implementing regulations (regulations, technical guides) and the Product Safety Act do not prescribe product quality requirements in terms of the product's possible environmental impact (Directive 2001/95/of t, 2001, Council Regulation (C), 1993). It is therefore necessary for the certification process to set uniform quality requirements that a product must meet for certain uses. The main subject of this paper is the examination of new possibilities of solidification/stabilisation (S/S) of waste neutralisation sludge. Neutralisation sludge can be characterised as waste arising from the neutralisation of waste acids from industrial production containing dangerous substances. The sludge is produced in large quantities and the cost of its disposal is enormous. This is why the efforts to use some of the neutralisation sludge have to some extent been long-lasting, starting 50 years ago. One of the first industrial products from neutralisation sludge was neutralisation sludge stabilised by fly ash from separators, which was deposited in the landfill as ordinary waste, thereby reducing the cost of landfilling (Keefer and Sack, 1978). At present, the handling of neutralising sludge is still, in most cases, tackled differently and often does not address its long-term storage or long-term stability. Although numerous methods have been used to treat neutralisation sludge, they have generally not been sufficiently evaluated, and the results of the monitoring of how neutralisation sludge behaves after the treatment are unknown.

Several research studies have been conducted to explore stabilisation and solidification (S/S) techniques for sludge containing metal hydroxides (Banaszkiewicz and Marcinkowski, 2008, Ivšić-Bajćeta et al., 2013, Chang et al., 1999, Conner and Hoeffner, 1998a, Tseng, 1998, Karamalidis and Voudrias, 2008). Neutralisation sludge is produced by neutralising acid waste water, in most cases by whitewash suspension (a product made from hydrated lime and water). This neutralising agent is widely used.

The frequent use of lime is based on its low cost and high efficiency for heavy metal precipitation in an alkaline environment, and its relatively easy preparation and handling of a neutralising suspension (Aubé et al., 2003). In some cases, powdered calcium oxide without prior hydration is added to the acid wastewater stream; however, this is rarely used in practice.

A common by-product of neutralising precipitation using whitewash is gypsum (calcium sulphate dihydrate). Gypsum comprises the largest proportion of the neutralisation sludge and contributes significantly to the total volume of the generated neutralisation sludge (Zinck, 2005).

At present, the handling of neutralisation sludge is, in most cases, solved individually and often does not address long-term storage issues or even long-term stability. Numerous methods have been used to handle neutralisation sludge, but they have generally not been sufficiently evaluated. The results of monitoring how the neutralisation sludge acts after treatment are also unknown. In the search for the most appropriate way of handling neutralisation sludge, the specific conditions at the site of neutralisation sludge must be taken into account. The major factors are the amount of sludge being created, sludge dewatering capacity, sludge dry residue, sludge volume, chemical and physical stability of the sludge, sludge composition, availability of the site where the sludge could be disposed of or used, and disposal costs.

After treatment, for example solidification, the neutralisation sludge can be used again provided that the material property demands set for the specific use are met. Potentially feasible and beneficial is the use of such treated waste as a structural or technological material for the closure and recultivation of landfills.

Within this paper, the effectiveness of metal immobilisation in the treated neutralisation sludge is investigated. The process of reprocessing produces a solidification product (the original hazardous waste – neutralisation sludge – is treated by suitable solidification agents), which prevents leaching of hazardous substances into the environment. Solidification describes the various effects of agents for the immobilisation of hazardous components. It changes the physical and mechanical properties of the waste. Stabilisation causes chemical changes of the hazardous components in the waste. The changes reduce solubility, mobility, and the components’ toxicity. A possible future use of the solidification product is during the building of the construction elements of the landfill body (fill slope, roads, levelling layers) to reduce the material that would otherwise have to be delivered to the landfill from the primary source.

In this particular case, which is presented in the paper, the S/S technology was used for reprocessing of waste. This technology is increasingly being used for treating waste generally. S/S is also a suitable technology for the treatment of neutralisation sludge, as using the right binders, additives and their relative proportions makes it possible to convert waste into inert material independently of the solubility of individual metals.

In addition to the ecological benefit, the subsequent use of waste neutralisation sludge provides a considerable economic benefit – the cost savings for the customer consist mainly of a considerably lower cost of waste takeover (up to several thousand Euros/tonne) and the possibility of using recultivation material for construction purposes directly at the site of recultivation, especially when remediating neutralisation sludge storage. The environmental benefit in this case is the limitation of the movement of waste outside the sanitised site and the limited displacement of the materials needed for the backfill, which will lead to lower dust and noise levels around the transport routes and thus the improvement of the environment.

Primarily, the main topic of the manuscript is an examination of the efficacy of S/S sludge treatments; however, this cannot be done without proper testing of S/S products for the possibility of their further use as a building material. Unfortunately, the testing procedure is missing in the national legislation. Therefore, the topic of the tests that should be applied in the investigation of treated waste for use as a building material is also investigated.

Section snippets

Materials and formula composition

The neutralisation sludge used in the experiments was waste sludge from the physical and chemical processing of a dangerous substance from an active industrial source. The neutralisation sludge that was used is listed under catalogue code 190205 – Sludges from physical and chemical treatment containing dangerous substances. This waste is generated during the production of steel galvanised wires in a neutralisation station which serves as a treatment of the pH value of sewage water. The waste

Unconfined compressive strength test

The UCS of the samples which was determined after 28 days of sample maturation gave strength of 0.8 MPa and a density of 990 kg/m3. From the point of view of the established limits (see section 2.2.1), sufficient UCS was achieved. It is a well-known fact that the increasing strength of the resulting solidification product is connected with the increasing amount of cement in the matrix.

The minimum common standard for compressive strength in the Czech Republic is 0.4 MPa for the additive

Conclusions

The aim of the scientific research presented in this paper was to investigate the possibility of using the solidification product prepared from the selected neutralisation sludge. A structural or technological material during the construction of the carrier and sealing elements of the landfill (dam, roads, underlay) seems to be the most advantageous utilisation of the solidification product. This will save material that would otherwise need to be delivered to the landfill from the primary

Acknowledgements

The paper has been prepared with the financial support of the project CSF 14-31248P “The study of the inbuilt hazardous waste impact on the cement matrix properties” and the project No. LO1408 “AdMaS UP – Advanced Materials, Structures and Technologies”, supported by the Ministry of Education, Youth and Sports under “National Sustainability Programme I”.

References (43)

  • K.P. Banaszkiewicz et al.

    Application of Hydrated Lime and Fly Ashes in the Process of Neutralisation of Wastes from Electrocoating with Portland Cement, Technical Magazine CH, Z2-CH

    (2008)
  • D.L. Bish et al.

    Thermogravimetric analysis of clay minerals

  • V. Černý et al.

    The use of energy by-products particularly in the production of fly ash aerated concrete

  • J.E. Chang et al.

    Stabilisation/solidification of sludges containing heavy metals by using cement and waste pozzolans

    J. Environ. Sci. Health

    (1999)
  • J.R. Conner et al.

    A critical review of stabilisation/solidification technology

    Crit. Rev. Environ. Sci. Technol.

    (1998)
  • J.R. Conner et al.

    The history of stabilisation/solidification technology

    Crit. Rev. Environ. Sci. Technol.

    (1998)
  • Council Regulation (EEC) No 339/93 of 8 February 1993 on Checks for Conformity with the Rules on Product Safety in the...
  • Decree of the State Office for Nuclear Safety No. 307/2002 Coll., on Radiation Protection, as Amended (In Czech...
  • Directive 2001/95/EC of the European Parliament and of the Council of 3 December 2001 on General Product Safety, Text with EEA Relevance

    (2001)
  • Directive 2008/98/EC of the European Parliament and of the Council of 19 November 2008 on Waste and Repealing, Certain Directives, Text with EEA Relevance

    (2008)
  • B. Dohnálková

    The research of the waste sludge with the content of hazardous substances solidification using cement matrix

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