Sua (Sowa) Pan, Makgadikgadi Basin, Botswana

The Sua (Sowa) Pan is a large flat natural topographic depression or drainage sump that is the deepest in a three-pan complex separated by dune-covered ridges. The other two being Nxai and Nwetwe pans that together cover around 24,000 km2, making it one of the largest playa complexes in the world. The term Sowa means salt in the language of the local San bushmen.

Pan surfaces are made up of brine-saturated sand and clay layers, with surface efflorescences of halite and trona. The main Sua pan is seasonally flooded by the Nata River and has a trona brine processing plant that commenced operations in 1991.

Today, Sua Pan is a seasonal salt lake or saline pan: it fills with water during the summer rainy season and retains water until April for May. Occasionally during the short wet season (December–March) surface water enters the saline environment and precipitates mostly calcite and halite, as well as dolomite and traces of other salts associated with the desiccation of the lake.

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Soda ash concentration pans

Its surface is underlain by a shallow water table composed of a hypersaline subsurface pan brine (up to TDS 190,000 mg/L) that is homogenous across much of the pan, with minor variations due to pumping by BotAsh mine (Botswana Ash (Pty) Ltd.),. The processing plant  extracts 2400 m3 of brine/h from a depth of 38 m. There is a notable local decrease in TDS as the pumping rate increases which may be indicative of subsurface recharge by less saline water. Isotope chemistry for Sr (87Sr/86Sr average 0.722087) and S (δ34S average 34.35‰) suggesting subsurface brines have been subject to a lithological contribution of undetermined origin. Recharge to the subsurface brine from surface water flooding including the Nata River appears to be negligible (Eckardt et al., 2008).

Botash plant

The BotAsh Company (half-owned by the Botswana government) operates a brine plant in the northern part of the pan and currently produces ~ 300 kty of soda-ash and 600 kty of halite for South African market (see Warren, 2016; Chapter 12 for a more detailed literature compilation). In addition to producing sodium carbonate salts using a variation of the Solvay Process, the plant also produces halite and sodium sulphate. The salt-cake (sodium sulphate) is a viable byproduct of the trona operation whenever market prices make it economic.


Sua Pan edge

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