Manila (AFP) - Philippine President Rodrigo Duterte on Thursday blamed "lobby money" for the downfall of his outspoken environment secretary Regina Lopez, who earned the ire of the country's mining industry after accusing it of corruption.

Despite his widespread popularity and hardline posture, Duterte said he was helpless to save Lopez from failing to be approved as a cabinet member by lawmakers in congress.

"It's a pity about Gina. I really liked her passion," he said, referring to Lopez by her nickname.

"I made a pitch for her but you know how it is. This is a democracy and lobby money talks. I do not control everything," he told a gathering of doctors.

He did not specify who lobbied against Lopez or who he would appoint to replace her.

The Commission on Appointments rejected Lopez's appointment on Wednesday, in a big victory for the mining industry.

Lopez sent shockwaves through the industry during her 10 months as environment chief, seeking to shut down roughly two-thirds of the nation's existing mines and banning any new open-pit operations.

Although Duterte's allies control both chambers of the Philippine legislature, the commission chose to reject Lopez.

Lopez has vocally blamed "big business," for her rejection, saying many who voted against her were representing mining interests.

She had previously sought to shut down 28 of the nation's 40 mines and cancel the contracts of dozens of others.

Last week she also announced the ban on new open-pit mining, which would have sounded the death knell for one of the world's biggest planned copper projects in the south of the country.

With the Philippines being the world's biggest supplier of nickel ore and a major source of copper, Lopez's campaign had impacted global prices.

Mining Inc had run a high-profile campaign to have the commission reject her, arguing she was jeopardising the lives of 1.2 million people who were dependent on the industry.

Even Finance Secretary Carlos Dominguez, a former mining executive whose family has big investments in the industry, opposed her, taking the unprecedented action of testifying against a fellow cabinet member at the commission hearings.

However environmental groups expressed outrage at Lopez's rejection, saying it showed Duterte had misled with his pledges to lead a government for ordinary Filipinos rather than the elite.

Congress rejecting a president's cabinet appointment is extremely rare in Philippine politics.