the present invention concerns process for obtaining melamine at high purity characterized by comprising the steps of :— quenching a melamine melt , deprived of off - gases of the melamine synthesis and containing melamine impurities such as ammeline , ammelide and polycondensates , with an aqueous solution comprising ammonia under conditions such to substantially convert polycondensates into melamine , obtaining a melamine solution substantially free of polycondensates , recovering melamine from said melamine solution by melamine crystallization , obtaining melamine crystals and a melamine crystallization mother liquor ,— treating said crystallization melamine mother liquor under conditions such to convert at least a portion of its ammeline content into ammelide and melammine , obtaining a treated mother liquid having at least a reduced ammeline content . the invention also concerns a high - pressure non - catalytic plant for the production of high - purity melamine implementing the above process and apparatuses suitable to be used in this plant .