* Dangote sells 416 mln Dangote Cement shares to foreign buyers
* Dangote Cement working to boost minimum share float - source
* The cement maker plans to double size of African plant by 2020 (Adds closing share price, stock index)
LAGOS, Aug 1 (Reuters) - Nigeria's Dangote Industries Limited sold a 2.3 percent stake in Dangote Cement to foreign investors on Tuesday in a stock market deal valued at 86.1 billion naira ($236 million).
Africa's biggest cement maker has been selling small stakes to increase its free float, which is well below the Nigerian stock exchange's required level.
A spokesman for the Nigerian Stock Exchange said 416 million shares of Dangote Cement were sold on Tuesday at 210 naira each in six off-market deals negotiated between Stanbic IBTC and Meristem stockbrokers.
The price was below Dangote Cement's closing price on Monday of 223.75 naira. Shares in the company, owned by Africa's richest man Aliko Dangote, jumped after news of the share sale, closing up 7.3 percent at 240 naira, valuing the company at 4.09 trillion naira ($11.2 billion).
A spokesman for the cement maker said the deal was between Dangote Industries Limited and some foreign investors, whom he did not identify.
The transaction increases Dangote Cement's free float to 10.4 percent according to Thomson Reuters calculations, still well below a stock market requirement of 20 percent.
It is the biggest company on the Nigerian Stock Exchange, accounting for a third of the bourse's total market capitalisation, and when it listed in 2010 the bourse waived its free float requirement because it wanted to encourage more companies to list.
It gave Dangote 18 months to reach the 20 percent level but a banking source said the company has still yet to meet its minimum float requirement as local investors dislike its high valuation and foreign investors have been deterred by a currency crisis in Nigeria.
In 2013, Dangote Industries sold 1.5 percent of its 95 percent stake in Dangote Cement to South Africa's Public Investment Corporation (PIC) for $289.3 million.
Subsequently it sold a 1.4 percent stake to Sovereign fund Investment Corp of Dubai (ICD) for $300 million in 2014.
Dangote Cement told Reuters last month that it planned to invest about $4 billion over the next two to three years to nearly double its production capacity to 80 million tonnes in Africa.
However it faces competition in Africa from French cement maker Lafarge which has combined its Nigerian and South African businesses to accelerate growth on the continent, as well as other local rivals.
Last week Dangote Cement reported a 24.6 percent rise in half-year pretax profit to 155.58 billion naira.
($1 = 365.00 naira) (Editing by David Evans and Susan Fenton)