Lokotrack Central and Hanson show a lot of bottle

A Lokotrack LT1213 track-mounted impact crusher on hire from Lancashire Crushing is being used to turn recycled glass into a tarmac ingredient for roads on and around the Isle of Anglesey, North Wales. The machine, which was supplied by England and Wales Lokotrack dealer Lokotrack Central, is crushing bottles, jars and other glass products into a sand substitute at Hanson Aggregates’ Caer Glaw Quarry at Gwalchmai, Anglesey.

The 44ha quarry had previously been a key supplier of Precambrian granite but quarry operations were halted and the site mothballed with only the site’s tarmac plant remaining operational. This left Hanson Aggregates with a problem. ‘As a company, we have a policy of conserving mineral stocks anyway, but we face a constant challenge from Northampton northwards in that there is very little natural sand that can be used in aggregate or tarmac products,’ said quarry manager Gary Kitson. ‘We have, therefore, been running experiments in which the sand was replaced with recycled glass.’

The recycling of glass into a tarmac product has been fuelled by Hanson’s acquisition of Packaging (Waste) Recovery Notes (PRN), a certificate issued by an accredited reprocessor when waste has been recycled or recovered within the UK. ‘PRNs are evidence that waste has been recovered or recycled and they’re big business,’ said Mr Kitson. ‘Businesses are keen to sell the PRNs because that absolves them of responsibility for the waste materials and we are keen to acquire them as it affords us access to potentially valuable raw materials.’

PRNs do, however, carry with them a time limit during which waste materials have to be processed, reused or recycled. ‘We currently have a stockpile of around 3,500 tonnes of glass waste and more is continuing to arrive at a rate of around 1,500 tonnes per month. We therefore needed a fast, effective and reliable way in which to process this material before we were hit with a PRN time penalty,’ explained Mr Kitson.

The waste glass had previously been processed using a cone crusher, but this had a habit of producing long shards that contaminated the recycled product. ‘Longer and larger pieces of glass retain heat which prevents the tarmac from solidifying. The replacement machine needed to be capable of consistently producing a –4mm product,’ said Mr Kitson.

The solution came in the shape of a Metso Minerals LT1213 impactor from Lancashire Crushing. The machine, which until recently had been tackling more traditional crushing duties processing sandstone for concrete applications, has to contend not just with glass but a whole host of contaminants.   

‘Although the waste is pre-screened, the feed material often still contains plastics and metal jar lids,’ explained Mr Kitson. ‘Thankfully, the LT1213 crushes everything in its path. The jar lids are removed by an overband magnet on the conveyor, while plastics and paper waste are segregated by an additional screening unit. Around 60% of the waste glass is processed in the first pass, but to ensure optimum quality and size reduction any oversized materials are reprocessed.’

The system clearly works as the LT1213 is currently processing the glass waste at a rate of around 180 tonnes/h, approximately 100 tonnes of which is suitable for use in tarmac base products.

For Mr Kitson, it is the culmination of many years of trial and error. ‘Hanson have spent years testing the process and the end product, and we now know it will work. Using this method is the best of both worlds; it helps conserve resources and increases recycling, but it is important to get it right. Not only do we need to provide a recycled product which solves a raw materials shortfall, but it has to be of equal, if not better, quality than the original, and this product is.

‘The material produced by the Metso impactor is of a very high quality, much better than dredged sand and much closer to home than our natural reserves. Use of this product makes economic and environmental sense.’