De Lange, who is also chairperson of Parliament's environmental affairs portfolio committee, spoke during a debate in the National Assembly on the department's R5.4-billion budget.
He said government would seek approval for lifting the ban at the 17th Cites conference, set to be held in South Africa in 2016.
"The data suggests that banning of legal, open trade in rhino horn has not resulted in reduced demand for the horn, and has not helped save the rhino from imminent extinction. Escalation in the slaughter of rhino is proof of this.
"Consumers simply do not believe that rhino horn has no medicinal value, no matter how many times we say so. Using increasingly sophisticated means, poaching syndicates have capitalised on the Cites ban to supply what appears to be a resurgent market demand," De Lange said.
More than 360 rhino have been killed by poachers in South Africa since the beginning of this year. Between 2007 and February last year the country lost 1460 rhino to poachers. South Africa is home to 83% of Africa's rhino, with 18 910 white and 2 044 black rhino.
The powdered horn, which finds an eager market in many Asian countries, is reportedly worth more, by weight, than gold, selling for as much as $65 000 (about R630 000) a kilogram.
De Lange said it was crucial that the possibility of legalising the trade in rhino horn be investigated.
"It seems abundantly obvious to me … that the rhino horn trade has been banned for 35 years, yet rhinos are still highly threatened and on the brink of extinction.
Surely it is time to devise new approaches.
"Legalising rhino horn trade for South Africa is likely to shift the market out of the hands of organised crime into legal channels, which must be good for rhino and other wildlife currently moving through these illicit channels.
"A large and steady supply of horns is also likely to lower and stabilise prices, which also plays against the black market," he said.
To effectively end, or at least contain, rhino poaching to acceptable levels required a "suite" of several carefully thought-out measures and interventions.
In the immediate term, there could be no substitute for heightened security using well-trained, properly-equipped rangers.
Expanding the ranges for the rhino also needed to be investigated.
"Whatever approaches are advocated, it should not detract from the fact that conservation of rhino still depends upon good old-fashioned protection, monitoring, [and] biological management of free-ranging rhino … ," De Lange said.
Cabinet agreed last year that dialogue should be opened on the "desirability and viability" of lifting the Cites ban on trading in rhino horn.
"While well-intentioned, this trade ban on legally selling rhino horn seems not to have saved any species or sub-species of rhino, while succeeding to drive the illegal selling of rhino horn underground."
The ban had created "a lucrative and well-functioning, illegal underground black market, which is a haven for organised crime, diverting vast sums of possible conservation funds into the hands of criminals".
Debilitating the black market
De Lange said that in its call to legalise the trade, government would only argue for a "limited and well-defined trade in rhino horn", within a strongly-regulated market mechanism.
The only horns to be traded would come from rhino that died of natural causes, or from present stockpiles, or from possible de-horning.
"No animals should be killed in the process," he said.
The portfolio committee viewed the existence of a lucrative, rapidly-growing black market trade in rhino horn as the "elephant in the room" when it came to discussions on solutions.
"In the committee's view, priority number one must be for the international wildlife conservation community to destroy or at least seriously debilitate this black market, and replace it with a strictly regulated market mechanism," De Lange said.
South Africa is reportedly sitting on a 20-tonne stockpile of rhino horn. At $65 000 a kilogram, this would be worth – at the current exchange rate – well over R10-billion. – Sapa