Chromite Beneficiation Kit
MATERIAL ECOLOGY RESEARCH & SPECULATION
PROTOTYPE OF A SMALL-BATCH BENEFICIATION KIT for CHROMITE ORE in the GREAT DYKE of ZIMBABWE
Cambridge, Massachusetts / 2015
Speculative design for a small-batch chromite beneficiation kit to support greater democratization of the value chain behind the stainless steel industry in mining operations. Perhaps enabling individual contract miners to capture more of the value of their labor through small-batch benefication (removing waste material from ore to concentrate valuable minerals), workers might gain a higher quality of life as well as more power and agency in global chromite supply chains, a key bottleneck in the global supply chain for stainless steel. In turn, stainless steel is a key material
Kit includes tools to support the following benefication processes :
3. magnetic seperation (chromite is weakly ferrous)
4. shake table sifting
5. spiral separation
Under current social, political, and economic conditions, the majority of the chromite ore extracted by tribute miners along Zimbabwe’s Great Dyke will be smelted down into ferrochrome by one of the two corporations that own the vast majority of the region’s mineral claims. This smelting process concentrates chromium content from 10-20% up to 60-70%, converting the bulky ore into an efficient commodity for global trade.
Based on design speculation to decentralize the concretation of control over chromium, I imagine dissolving the current duopolistic claims structure to enable the individual miners to lay claim to the fruits of their own labor. With the claim structure thrown open, miners are also in the position to capture more of chromite’s value chain, increasing its concentration before selling it into the stainless steel industry.
Ferrochrome smelting is an extremely energy intensive process demaning 3000 degree temperatures, out of scale for individual tribute miners’ operations. To avoid re-creating concentrations of power thereby implicated in smelting, mineral beneficiation offers a range less energy-intensive methods to increase chromium concentration. Benefeciation is largely a process of mechanically seperating chromite (or any mineral) from surrounding dirt and other unwanted material (known as ‘gangue’).
Beneficiation is already practiced at some locations along the Great Dyke at industrial scale, using a range discrete machines. Given the crude mechanics behind many of these beneficiation techniques, it is possible for some of these machines to be translated into simpler devices, able to be produced with basic materials at smaller scale and lower cost. To consider how an individual tribute miner might undertake chromite beneficiation, this project identifies five key beneficiation methods that meets these preceding criteria.
After comparing a range of mechanical, chemical, and metalurgic beneficiation processes, I identified crushing, screening, magnetic separation, spiral concentration, and table shake seperation as viable methods for decentralized beneficiation. To materialize this investiagation, I designed a kit of tools for these processes, materially comparable to tools already used by tribute miners such as wheelbarrows and pick axes.
Once beneficiated, chromite ore may still be sold into relatively centralized global metals distribution channels. At the same time, there is a significantly decentralized production base for custom alloys and small local manufacturing that these newly equipped mineres could sell directly into.
CRUSHERbreaks down large chunks of material to more workble size
screens out pebbles, rocks, and other larger materials
ore mixed with water is sprayed across the table as lateral vibration coaxes denser chromits mineral to sink and catch along the tables ridges while lighter dirt and other gauge pass over the table and out into the waste water
chromite is slightly ferrous and so can be gently pulled out of gangue using strong magnets
using similar dynamics to the shake table, the spiral concentrator expands the surface area for material run-off, mitigating the need for shaking while still catching chromite in small grooves along the tool surface
For example, Wollaston Alloys located in Braintree, MA is a prototypical facility for small batch stainless steel production, capable of making direct use of the relatively small quantitite of chromite ore that would be produced by a given individual miner/beneficiator in the Great Dyke. Beginning with a base of scrap steel, shops like Wollaston Alloys would use an Argon Oxygen Decarburization furnize to decarborize the steel in small batches of roughly 5000 lbs (say, the size of a bathtub or two).
Given that the scrap may be of unknown or mixed carbon content, this process of removing all the carbon gives the shop a controlled batch of iron to work with, to which controlled quantitites of coke for carbon and other mineral ores can then be added back in to create the desired alloy for a given client. At a scale analogous to the miners’ operations in the Great Dyke, shop workers at Wollaston Alloys use simple hand tools like shovels to fold chunks of chromite ore into a batch of stainless steel, perhaps being cast into a new machine part for a local factory.
In the long run, with fewer middle men required in the chromite trade, it is conceivable that the global price of stainless steel could be brought down, make it cheaper and more accessible for everyone, helping to flatten the advantage given to industrial scale food processing operations over small producers discussed in Part I. Over time, a leveled playing field might help build constituency to resolve the conflict between food safety regulations built on stainless steel and designs scaled to a diverse range of food producers and processors