2018
CONCENTRATION
John Dorr
ohn Van Nostrand Dorr was born in Newark,
New Jersey, in 1872, He graduated from
Rutgers in 1894, with a B.S. in chemistry and
became chemist at a smelter at Deadwood,
South Dakota, in the Black Hills. This was a
period of great developments in metallurgy,
when the refractory gold ores of "The Hills"
were being treated by smelting, chlorination,
and the newly developed cyanide process. In
1902, he formed a partnership with John
Lundberg, a mine leaser, to operate a cyanide
mill, the Rossiter mill, to treat gold ores from
Lundberg’s two leaseholds, the Buxton and the
Bonanza mines. In 1903, the partners purchased
the two mines, erected a 100-ton per day
(91 t/d) wet crushing cyanide mill on the site,
and took in a third partner, AD Wilson, a civil
engineer. At the Lundberg, Dorr & Wilson mill,
Dorr tried out the new Moore filter process, a
large cone for the continuous collection of
slimes, and a Chile mill in place of the stamps
used in the district. To affect a clean-cut
separation between fine slimes and coarse
sands prior to separate cyanide treatment, the
Dorr clarifier was developed, patented, and
arrangements made for its manufacture. The
clarifier became the Dorr classifier.
Wet ball mills were being tested on the gold
ores in South Africa and copper ores in Arizona
and the Dorr classifier made continuous closed
circuit grinding a reality. The ball mill – rake
classifier circuit (spiral classifiers were also
used) was used for 50 years until the
development of better pumps enabled
hydrocyclones to replace mechanical classifiers.
John Dorr invented other machines which
were widely used for processing minerals, for
example the Dorr continuous thickener and the
Dorr agitator, but it was the classifier which
transformed the technology.
John Dorr was one of the great inventors of
methods to process solid particles and he was
quick to take these methods from ideas to
operating practice.
1 – In 1906, Dorr was engaged as consultant
on the remodelling of the dry crushing mill of
the Mogul Mining Co, which was having trouble
with slime collection. He conceived the idea of
continuous slime thickening in flat-bottomed
tanks and developed the first Dorr continuous
thickener. In 1910, came the Dorr agitator and
later two new principles: continuous
countercurrent decantation and closed circuit
grinding. The engineering principle underlying
these inventions was that mechanical means
were necessary for most efficient continuous
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handling and treatment of finely divided solids
suspended in liquids. Manufacturing
arrangements were made in Denver and Chicago
and Dorr began to build an engineering
organisation to market his inventions and the
engineering services that went with them, while
continuing to manage two mining properties in
the Black Hills. In 1910, the Dorr Cyanide
Machinery Co was formed to become in, 1916,
the Dorr Co Engineers.
2 – The technological developments in ore
dressing and wet metallurgy during the 1920s
greatly increased the demands for Dorr
machinery and engineering services in this
country and abroad and territorial growth
began. The Dorr Co built offices in many cities.
Originally the company’s business was related
directly to the cyanidation of gold and silver
ores in this country and in Mexico. The iron,
lead, copper, phosphate, and sand fields were
also entered in a small way. Ultimately not only
all of wet metallurgy, but also most of heavy
chemical and industrial processing, sugar
manufacture, and sewage, water, and trade-
waste treatment, became Dorr customers.
3 – The loan in 1914 of a small experimental
thickener to Chicago's Sanitary District led to a
vast new field which in normal times amounts to
about one-third of the company’s business. The
initial objective was the continuous clarification
of domestic sewage. The clarifier, an adaptation
of the thickener principle, proved to be the
solution. Intensive studies of this new field
resulted in the development of a complete line
of special equipment, which has been found to
be directly applicable to the treatment of
municipal sewage and water supplies, and to
liquid industrial wastes and sources of process
water. The three original machines, produced
with only a nominal development cost, have
been expanded to over 30, of which there are
over 75 different types. However all are
inherently based on the same fundamental
principles involving classification,
sedimentation, and agitation.
4 – John Dorr, in association with Francis
Bosqui, published two editions of “Cyanidation
and Concentration of Gold and Silver Ores”. This
was a seminal book for mineral processors.
History of Dorr-Oliver
1904 Dorr Company
founded by Dr John Van
Norstrand Dorr, 1872-1962.
Began his career at 16 years
of age working in the
laboratories of Thomas Alva
Edison
1907 Oliver Company founded by Dr Edwin Letz
Oliver, 1878-1955. A Californian from San
Francisco and a graduate of the University of
California
1914 The Sanitary District of Chicago installs a
new Machine called a Dorr Clarifier
1916 The first DORRCO™ suction pumps are
built
1919 Dorr develops the washer and slurry mixer
1920 Dorr develops the Cane Juice Clarifier and
sells the first one through a Representative in
Havana Cuba
1921 Dorr develops the Olivite ® Centrifugal
Pump
1923 Dorr develops Rectangular Clarifiers for
Sewage Treatment
1925 Dorr develops Washing Tray Thickener and
opens overseas offices in Paris and Berlin
1927 Dorr designs the Detritor ® for Sewage
Degritting
1931 Dorr and Oliver merge. Dorr establishes a
facility in The Hague, Netherlands
1933 Dorr establishes representation in India
1934 Dorr and Oliver dissolve
1935 Dorr develops the Torq Thickener
1937 Dorr develops a combination Washing Type
Tray Thickener
1938 Dorr develops the Siaker
1954 Dorr and Oliver merge for the second time
1955 Merrill Company acquired and adds the
Merco ® Centrifuge
1968 Dorr-Oliver introduces the Cabletorq ®
Thickener. Curtis Wright acquires majority stock
in Dorr-Oliver
1969/1970 ODS ® Spring Assist and Air Cylinder
assist introduced to the market
1979 Curtis Wright completes acquisition of
Dorr-Oliver
1981 Kennecott acquires Dorr-Oliver: Kennecott
and SOHIO merge
1987 Contor Holdings, a Canadian company,
acquires Dorr-Oliver and Keeler Boiler
April, 1988 Leveraged buy-out by Dorr-Oliver
management
May, 1995 Krause-Maffei, Germany, acquires
Dorr-Oliver
Sep, 1999 GL&V, Montreal, acquires Dorr-Oliver
Sep, 2000 Hazleton, PA, manufacturing closed
Nov, 2002 GL&V purchases Eimco, Salt Lake
City, UT; Dorr-Oliver and Eimco are integrated
Aug, 2007 FLSmidth Minerals acquires Dorr-
Oliver Eimco
Supplement International Mining | JUNE 2019 HoF 11