He discusses the genesis and nature of silver ores, the dry refining process: smelting of silver ores and its impact on the environment, the wet refining process: the chemistry of the patio process
, the physical infrastructure of the patio process
, the Hacienda Santa Maria de Regla, the patio process
and smelting at Regla, the economics of refining silver, and the environmental impact of silver refining: a shift of paradigm.
The Spanish discovery of the cinnabar deposit at Huancavelica, Peru around 1560 proved vital for the prosperity of silver mining in the New World because the "patio process" for the amalgamation of silver ores (invented in Pachuca by Bartholome Medina in 1554 and used widely in the New World thereafter; see later) required mercury.
Before the advent of the patio process, these ores were simply roasted out of the veins, then reduced in crude furnaces: one observer wrote that "the Peruvians get the silver by burning the hill, and, as the sulfur stone burns, the silver falls in lumps" (Rickard, 1932).
Before the advent of the patio process, the Spanish in South America borrowed their ore-smelting technology from the Incas.
These early technologies were rendered instantly obsolete, and the whole Spanish-American mining industry took a quantum leap forward, in 1554 with the advent of the "patio process" for the amal-gamation of silver ores.
The success of the patio process meant that mining no longer was confined to near-surface bonanza ores; some lower-grade ores could also be worked economically.
The Patio Process is often mentioned but seldomly described in the metallurgical literature.
The patio process was not too well suited for northern climates where freezing was encountered and people were in a hurry.
The intent of this article has been to describe the ancient silver recovery methods, especially the Patio Process. Some mention will be made of more modern processes.
Few textbooks on metallurgy give the chemistry of the Patio Process. It was located in a rather obscure chemistry textbook listed in the references.
Van Nostrand, 1954 (This is the reference containing the chemistry of the Patio Process.)
The patio process
for silver recovery originated in Mexico [ednote--the little-known chemistry of the patio process
is described in a special report on the older processes for silver recovery in next issue of E&MJ].