Reduced Infrastructure Requirements

NEUTRA-MILL WATER TEATMENT SYSTEM – CASE STUDY

ACID ROCK DRAINAGE – BENAMBRA BASE METAL MINE

• Difficult access
• Minimal infrastructure
• Acceleration of treatment process
• Aqueous metal concentrations lowered
• ph of 180 megalitres raised from 2.8 to 8.0
• Treatment precipitates automatically deposited into tailings pond
• Lowered cost of treatment relative to the existing conventional dosing system

LOCATION

North-Eastern Victoria, Australia. 260 kilometres north-east of Melbourne (Latitude: 37° 00′ S, Longitude: 147° 54′ E).

SETTING AND CLIMATE

The Benambra Mine is located in the highlands of Victoria. Mineralisation occurs at an elevation of 600m above sea level in the headwaters of the Tambo River. The local terrain is steep and heavily forested. Annual rainfall is in excess of 900mm, falling predominantly during the winter period.

CLIENT

Denehurst Limited.

BACKGROUND

Ore at the Benambra mine consisted of massive sulphide mineralisation containing copper-zinc ± lead. This material was crushed and beneficiated on site, and tailings material disposed to a nearby impoundment.

Once resources at the Wilga deposit had been depleted, Denehurst sought to terminate their mining activity at Benambra. Site closure was contingent on a number of factors, including the treatment and stabilisation of highly acidic wastewater in the tailings impoundment.

SITE ISSUES

Whilst the site was under “Care and Maintenance”, Denehurst used the processing plant’s existing conventional dosing system to dispense 2.5 tonnes of hydrated lime per 24 hours via a ˜1.0 km pipeline. This system was found to be expensive to operate (using a 100kW generator), required 3×2 man shifts operating on a 24 hour, 7 day/week basis, and was not providing adequate pH control.

WORK PROGRAM

A portable Multi Purpose Neutra-Mill was called upon to lower treatment costs and accelerate the neutralisation and demineralisation of 180 megalitres of acidic and metal-rich tailings liquor. Two site staff were employed for 8 hours/day, 5 days/week to dispense hydrated lime using a Neutra-Mill.

ADVANTAGES OF A MULTI PURPOSE NEUTRA-MILL

A Multi Purpose Neutra-Mill was available for mobilisation within 24 hours to address this issue. Being capable of operating directly within the tailings dam, the Neutra-Mill has very low power requirements (2.5kW) and avoids the need for pumping costs. The lower operating costs associated with these benefits made the Multi Purpose Neutra-Mill an ideal and cost effective solution for this acid water treatment task.

Despite its size, the Multi Purpose Neutra-Mill was capable of a significantly higher throughput of reagent than the on-site fixed-plant dispensing facility (see below).

RESULTS

The pH of the acidic tailings water reached a low of 2.8, and rose to approximately 8.0 after treatment with 176 tonnes of hydrated lime from the Neutra-Mill. An average of 4.0 tonne of hydrated lime was manually dispensed via 25 kg bags through a Multi Purpose Neutra-Mill and into the tailings dam during each 8 hour working day. The dosing regime formed only one part of a site maintenance program for the staff of two men. Treatment was completed in less than 2.5 months.