African Potash has taken a step forward in its bid to develop a mine in the Republic of Congo.The company's shares rose 0.38p, or more than 14%, to 3p at 14:36 in London as it began an environmental and social impact study at its Lake Dinga project before drilling starts next year. Potash is used to make fertiliser.Chief Executive Edward Marlow said: "Lake Dinga is located in a well-recognised potash district and is surrounded by several world-class projects including Elemental Minerals' Sintoukola project."PW