One of his best known works, Sunflower Seeds, consists of about 3.3 million porcelain "seeds" (5 tons), being each individually hand-painted in the town of Jingdezhen by 1,600 Chinese artisans, and scattered over a large area of the exhibition hall.
Originally, the artist was keen for visitors to walk across and roll in the work to experience and contemplate the essence of his comment on mass consumption, Chinese industry, famine and collective work. However, on 16 October, Tate Modern stopped people from walking on the exhibit due to health liability concerns over the porcelain dust.
In February 2011, a 220-pound (100 kg) pile from Sunflower Seeds sold for $559,394 (well above its high estimate of $195,000) at Sotheby's in London. In May 2012, Tate Modern acquired 8 million of Ai's "Sunflower Seeds" with support from the Art Fund, although the figure was not disclosed. (from wikipedia)
They now even pretend to turn this public site into church estate. They actually have already banned the term Mezquita (Mosque) to impose religious monopoly, while the Mezquita is actually one of the few great universal paradigms of harmony between cultures (main reason why it was declared World Heritage in the first place).