Andacollo: A place where the extraction of gold and faith meet

Rodolfo Marin Rivera

1Andacollo, a town on the fringes of Chile’s Atacama Desert, has a long pre-Hispanic history, and it is today known not only for its massive festival honouring the Virgin of the Rosary, but also for its gold mining history.

About 90% of the population is involved in mining activities. Many are generations of miners committed to extract hope from the deep earth day after day.

2The mining history of Andacollo is related to the invasion of the Incas that mainly happened before that the Spaniards were conquering Chile. 500 years ago, the Incas were the first to extract gold from the mountains close to the town. Nowadays, the mining activity is carried out by the so-called “pirquineros” (miners) that work independently in small and artisan operations using ancient techniques and tools that are not so different from the ones used by their ancestors. The minerals continue being extracted from the mountains not so far from the town, where the gold grade is very low and it is located in “veins” very deep in the earth, making the work difficult and extremely dangerous. The pirquineros appeal to their faith and devotion to the Virgin, and ask for protection and health to extract the precious metal from the bowels of the Earth.

3Nowadays, the scanty pirquineros that still remain in the town, still continue performing the process of grinding minerals in “maray” and “trapiches”. Gold is recovered by the amalgam formed with mercury during or after continuous milling.

Both milling devices are pre-hispanic techniques that have been adapted to recover gold. The “maray” are handcrafted systems used by the Incas to grind corn, wheat and barley, adapted by the Spaniards to grind minerals. It is driven by hand using a grinding cylindrical stone that rests on a cup, which in the past was made of stone and now concrete. It is still possible to see it in the courts of some houses.

4The “trapiches”, similarly to the “maray”, are a sophisticated mechanical system used to grind gold minerals, which are in use since the end of the XIX century. It is a kind of circular tray full of water, on which the miners turn two heavy wheels to grind the mineral. Coarser particles of gold are recovered at the back of the “trapiche” caught by the amalgam formed with mercury. Middle size particles of gold are collected at the edges of metallic sheets made of copper and mercury alloy. The finest gold particles are collected and re-washed by a flotation process.

Mercury is used extensively during the rustic gold mining, so that a mercury-gold amalgam is formed. The gold is produced by boiling away the mercury from the amalgam. Mercury is effective in extracting small gold particles, but the process is hazardous due to the toxicity of the vapours. Today, new technological processes based on nitric acid or aqua regia have been developed, but their application is only economically feasible at larger scales.




3D-Printing human tissues using cellulose: will science fiction become reality?

Carmen Piras

imagesMost of you have probably heard about the Frankenstein’s monster, a novel written by the English author Mary Shelley. For those who don’t know it, it is the story of Victor Frankenstein, a scientist who invented a secret technique to impart life to unanimated matter. This technique allowed him to create a monstrous creature with human emotions and sensations.

This is of course only science fiction. However, nowadays, the on-demand growth of human tissues and organs using artificial instruments is becoming reality. One emerging manufacturing technique with promise in tissue engineering and regenerative medicine is 3D printing, which is based on the 3D deposition of material in specific shapes. This technology can be applied in biology (3D bioprinting) to produce 3D scaffolds of our tissues. The cells are directly embedded inside the scaffolds and different cell types can be distributed in different locations. The material loaded with the cells is then 3D printed into the desired shape. This method allows the fabrication of bone and cartilage tissues, skin and cardiac constructs and the regeneration of hepatic tissue.

One of the most important factors in 3D bioprinting is the choice of the material used as ink (or, more specifically, bioink), which should be biocompatible and allow cell survival during the printing process. Beside this, the ink should have an optimal viscosity to allow printing and to avoid the 3D printed shape to collapse. Water based gels (also called hydrogels) are ideal inks for 3D bioprinting. These materials are mainly composed of water (> 99 %) and therefore can closely mimic the natural environment of cells.

Hydrogels can be obtained from a wide range of molecules including natural derivatives such as gelatine, alginate, collagen, hyaluronic acid and cellulose. Being an abundant, renewable, low-cost resource, cellulose represents an ideal candidate for the production of hydrogels for 3D bioprinting. This molecule is formed of long glucose chains and it is obtained by extraction from plants or can be produced by bacteria. Mechanical and chemical treatments of raw materials allow the extraction of cellulose in the form of nanofibers or nanocrystals. The suffix nano- refers to the fact that the extracts have one dimension (length or width) in the nanometre range (1.000.000 smaller than 1 mm).

UnknownA variety of bioinks based on cellulose nanofibers and nanocrystals has been created by a number of research groups. These could be applied for the regeneration of human tissues (such as cartilage) or to obtain 3D printed drug delivery systems and wound dressings. Although very promising, this research field is still new and growing. We hope that in the future cellulose will be further exploited to develop new bioinks. Will this be the route towards a new Frankenstein’s monster? Stay tuned!

Want to know more about this? Read this article:



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