After consolidating its position, in 1970 it merged with another company, giving rise to the Unión Explosivos Río Tinto (ERT) group.

However, from the end of the 1920s, RTC's business declined due to the economic situation of the time, especially after the crash of 1929 and the subsequent arrival of the Second Republic.

[11] CEMRT came to control all the installations in Huelva, the railway line,[12] the pier, the country estates and the mining concessions held by RTC throughout Spain.

However, the British maintained their presence in Huelva through their technical consultancy services and by developing the commercial activities carried out by CEMRT abroad.

From 1964 onwards, the company played an important role in the development of the Chemical Park of Huelva,[14] where it installed an electrolytic plant to obtain pure copper.

[17] CEMRT was also closely linked to the Sociedad Española de Construcciones Electromecánicas, in Córdoba, to which it supplied copper.

In line with the company's diversification policy, from 1964 onwards it held talks with foreign copper suppliers in order to meet its new chemical-industrial activities.