Beneficiation of tailing mounds containing ore

In flota­tion meth­ods, e.g. for the recov­ery of ores, fine mate­ri­als accu­mu­late with a min­er­al con­tent that for decades was too low for fur­ther ben­e­fi­ci­a­tion to be per­formed in a cost-effec­tive man­ner. The mate­ri­als were deposit­ed in tail­ing ponds or in waste dumps, where in many cas­es mil­lions of tons accu­mu­lat­ed over the years. Today – in a time when raw mate­ri­als are scarce and high-qual­i­ty ore is increas­ing­ly rare – ben­e­fi­ci­a­tion of the dumped gangue mate­ri­als often makes com­mer­cial sense, par­tic­u­lar­ly as they often rep­re­sent an eco­log­i­cal risk. This can be done cost-effec­tive­ly with the aid of Eirich mixers.

Ores and oth­er use­ful min­er­als occur in nature almost entire­ly in a con­t­a­m­i­nat­ed form. For use as a raw mate­r­i­al, the gangue needs to be sep­a­rat­ed. Since the start of the 20th cen­tu­ry, the flota­tion method has been the pri­ma­ry way to extract the raw mate­ri­als. The sub­stances that are to be sep­a­rat­ed are ini­tial­ly ground down to a size that is small enough so that the indi­vid­ual com­po­nents exist as phys­i­cal­ly sep­a­rate grains. The mix­ture is then sus­pend­ed in an aque­ous solu­tion and aer­at­ed with a tur­bu­lent gas flow. Under the addi­tion of aux­il­iary mate­ri­als, it is then pos­si­ble to bind min­er­al gran­ules to gas bub­bles, which then rise to the sur­face where they can be skimmed off as froth. The oth­er par­ti­cles (referred to as the flota­tion tails) remain in the tur­bid slur­ry or form a sed­i­ment at the bot­tom of the flota­tion cell and are then pumped for dis­pos­al into so-called tail­ing mounds. The rock that accu­mu­lates dur­ing min­ing and the rock that is co-extract­ed in the process, which is sep­a­rat­ed out dur­ing ben­e­fi­ci­a­tion, forms these mounds.

In the past, ben­e­fi­ci­a­tion of dumped fine tail­ings, which often rep­re­sent a risk for the envi­ron­ment, was often not cost-effec­tive. Even mechan­i­cal dewa­ter­ing was too com­plex and expen­sive. Now though, high-per­for­mance mix­ing tech­nol­o­gy makes pos­si­ble cost-effec­tive ben­e­fi­ci­a­tion of flota­tion tail­ings that still con­tain a sig­nif­i­cant lev­el of usable min­er­als – and this even with vary­ing mois­ture con­tents. In order to extract the min­er­als, the gangue mate­ri­als usu­al­ly need to be mixed with one or more oth­er mate­ri­als and gran­u­lat­ed. Suit­able mix­ing and gran­u­la­tion tech­nol­o­gy is required for this.

The mix­er has proved itself in count­less appli­ca­tions. It has been in use for decades in a wide range of indus­tries for all kinds of mix­ing and gran­u­lat­ing tasks, par­tic­u­lar­ly for appli­ca­tions demand­ing a high qual­i­ty of mix. The unique work­ing prin­ci­ple of this mix­er nor­mal­ly enables very advan­ta­geous process con­trol. Thanks to the tech­nol­o­gy, it is pos­si­ble to process mate­ri­als of very dif­fer­ent types and con­sis­ten­cies with­out any prob­lems, for exam­ple in order to pro­duce gran­u­lates from slur­ries under the addi­tion of dry mate­ri­als. In the process, agglom­er­ates are dis­in­te­grat­ed in the best pos­si­ble way so that the end prod­uct offers an excel­lent qual­i­ty of mix, even if aux­il­iary sub­stances such as chem­i­cals are added in the ppm range. The good self-clean­ing effects and the sys­tem-relat­ed low wear of the mix­er are often impor­tant aspects.

In addi­tion to mix­ers that oper­ate on a batch basis, today we also see use of mix­ers that oper­ate con­tin­u­ous­ly. For exam­ple, it has been shown in the pro­cess­ing of tail­ing mounds from mag­ne­site pro­duc­tion that these mix­ers offer sig­nif­i­cant process and cost advan­tages. One of the advan­tages here is that – unlike in batch mode – there is no time need­ed for fill­ing and emp­ty­ing. In addi­tion, small­er mix­ers with low­er input pow­er can be used.

The sys­tem-relat­ed advan­tages of Eirich mix­ing tech­nol­o­gy also come into their own for oth­er recy­cling tasks, dur­ing waste pro­cess­ing, in land­fill engi­neer­ing and in the repro­cess­ing of con­t­a­m­i­nat­ed sites. Exam­ples include the agglom­er­a­tion of dust from steel­works for recir­cu­la­tion to the sin­ter­ing con­vey­or or for addi­tion to reduc­tion process­es, or for the agglom­er­a­tion of con­vert­er dusts con­tain­ing zinc for input into the Waelz process. Spe­cial mix­er designs are used for the pro­cess­ing of con­t­a­m­i­nat­ed soil or – in the form of so-called vac­u­um mix­ers – for the dry­ing of paint/enamel sludge with explo­sion pro­tec­tion (spray can recy­cling). Heat­ed mix­ers are avail­able for spe­cial appli­ca­tions (up to 250°C).