Stabilisation Solidification Treatment of Contaminated Soils using Steelworks Waste, Port Talbot by Celtic Technologies Ltd

Shortlisted Brownfield Awards Category 2 - Best Scientific/Technical/Digital Advance

Introduction

Stabilisation/solidification (S/S) of contaminated soils has been proven to be an effective and durable remediation technology. The technology has broad applicability to a number of sites. Pulverised fuel ash (PFA) is commonly used as an additive in S/S works with a cementitious product due to its low cost. PFA is produced by coal fired power stations. However, most of the remaining UK coal fired power stations have been closed with the few remaining power stations scheduled for closure soon. Due to the move away from coal fired power stations, an additive commonly used for the S/S treatment of soils has become scarce and will soon be unavailable.


In 2018, Celtic began talking to Tata steel about remediation works for a new power plant on the Tata steel site in Port Talbot. Andrew Scott Ltd, the Principal Contractor initially carried out ground remediation works for the proposed power plant development. As part of this work, stockpiles of soil with coal tar and hydrocarbon impact were generated. Treatment options for the contaminated material such assoil washing and bio‐treatment were considered but were not technically feasible. Celtic identified that S/S treatment would likely be an effective remediation technology to enable reuse of the soils. The only other viable option was off‐site disposal of the contaminated soils which was prohibitively expensive.

Aerial Image of Site and Soils for Treatment

Tata had been actively seeking beneficial uses for steelworks wastes which often have limited or no recycling or re‐use potential. A steel making waste produced by Darlow Lloyd & Sons from a waste recovery plant within the Tata works was identified that could potentially be used as an S/S additive. The material is currently stockpiled onsite prior to disposal and has very limited options for re‐use. This waste has, we understand, never previously been used in contaminated land treatment. Celtic began researching and trialling the use of steelworks waste for the treatment of contaminated soils from the remediation works in late 2018.

Stockpiles Soils with Hydrocarbon Impact Prior to Treatment

Conclusions

 

Celtic have technically advanced remediation works by selecting and demonstrating that an alternative additive for use in S/S treatment works is effective. PFA was commonly used for S/S treatment works in the UK, however, its availability is reducing due to the phasing out of coal fired power stations. The steelworks waste trialled has been used for S/S works and testing has demonstrated that contaminated soils treated with the additive are durable and have very significant reductions in the leaching of contaminants – greater than 99.5 % reduction. Concentrations of contaminants in leach test eluate of samples from heavily contaminated soils meet Environmental Quality Standards for many contaminants.

 

The advance can have a broad impact across the remediation industry as it may be used for soils with typical contaminants such as hydrocarbons. In terms of cost, the additive is similar in value to PFA and in the region of 10-20% the cost of cement.

 

In this specific application, the use of a waste has saved some 7 tonnes of CO2 emissions compared to traditional additives and the use of S/S saved in the order of £750,000 compared to off-site disposal which was the only other viable alternative.

 

With the various elements of the trial/feasibility works, Celtic have been involved with the development of steelworks waste for use in S/S treatment for over two years. The works have included initial feasibility assessment, laboratory scale trials, discussions with statutory regulators, obtaining environmental permitry, full scale works and performance assessment on samples from the full scale works. To date the works have been positive at every stage and very rewarding with an effective full scale project carried out for Tata Steel. Very good performance data has been obtained from the full scale works. The use of the waste has also been beneficial in terms of waste reduction for the steelworks and sustainability. We look forward to the potential of using the waste for other remediation projects outside the steelworks at Port Talbot.

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