Modern Mining February 2015

PRODUCT News

Longi-Multotec offers new generation demagnetising coil Magnetic Separation business line.

requires an alteration of an applied mag- netic field from north to south, while monotonically decreasing the field inten- sity steps. This elimination of the magnetic hysteresis will bring about scrambling of the magnetic domains striving towards a zero net resultant charge.” DMS efficiency may be improved by lowering and then controlling medium viscosity as well as medium stability and density control. These improvements are clearer in cyclones, where gravitational forces are higher, compared to DMS drums. “Over the years, demagnetising coils have been developed to improve the fre- quency of alternating magnetic fields, as well as to decrease the distance over which the field is dissipated. These prod- ucts were aimed at allowing more energy efficient and compact designs. Ironically, however, this drive has led to inefficien- cies in process performance,” says Willem Slabbert, Applications and Process Manager at Multotec’s Solid Liquid and

Demagnetising coils are commonly used in the minerals processing industry to demagnetisemagnetised slurry. Themedia used in the Dense Medium Separation (DMS) process is magnetic to allow for sim- ple recovery and regeneration processes. In the past, traditional demagnetising coils have been plagued by inefficien- cies. Longi-Multotec now offers a solution that – it claims – addresses these issues and provides continuous, high frequency demagnetisation. “It is well known that recovery of the media by means of magnetic separators induces a residual magnetisation, which causes flocculation of the magnetised particles and increases the viscosity of the medium. It is possible to reduce or even eliminate these effects by demagnetising the magnetic over-dense product stream,” says Stuart Callum, Process Engineer at Multotec’s Solid Liquid and Magnetic Separation business line. “The process of demagnetisation

The constant wave, high frequency demagnetising coil has been designed to overcome the inefficiencies of previous generations of coils by generating a con- tinuous wave of a consistently decreasing magnetic field across distance in the direc- tion of fluid flow, at high frequencies of up to 200 Hz. This allows continuous demag- netisation of slurry through all consecutive slurry elements. “Even though the actual magnetic coil remains the same, new advances in electri- cal component technology allow improved control over the electrical energy supply to the coil. The performance advancement of the new generation Longi-Multotec demagnetising coil will allow more effi- cient demagnetisation, which will facilitate better viscosity management and in turn will improve cyclone performance in terms of separation efficiency and quality,” Slabbert concludes. Multotec Group, tel (+27 11) 923-6193

February 2015  MODERN MINING  47