Production of organic aminium lactates or diaminium di-lactates comprises:    (a) fermentation of carbohydrate-containing substrates to produce lactic acid;    (b) neutralisation of the lactic acid by addition to pH 4.5-13.5 of a non-toxic and non-deactivating amine or diamine;    (c) removing suspended substances and part of the dissolved substances from the fermentation medium;    (d) concentrating the fermentation medium, and    (e) recovering the crystalline racemic, optically active or optically inactive salt from the concentrate.    Also claimed are:    (1) diaminium di-lactates of formula (V);    (2) rac-, D- or L-imidazolium lactate and rac-, D- or L-4-dimethylamino-pyridinium lactate;    (3) the production of 1,4-dioxan-2,5-diones (I) by:    (i) reacting an a hydroxycarboxylic acid (II) or salt or hydrate in solution with a piperazine derivative (III) or salt (IV);    (ii) cyclising the (V) obtained (optionally after working up and recrystallisation at 60-80 C) in the presence of a catalyst at elevated temperature, and optionally    (iii) recrystallising the resulting (I).    R1, R2 = H or 1-10C alkyl;    R3-R10 = H; 1-10C alkyl; 1-10C alkoxy; aryl-1-10C alkyl; aryl optionally substituted by alkyl, alkoxy, aryl, halo, NO2, CN or sulphonyl; allyl; halo; CN; NC; or part of a fused aliphatic, aromatic or heteroaromatic system;    X = anion, preferably OH, halo, e.g. Cl, I, Br or F, acetate, HSO4, H2PO4, toluenesulphonate or a group derived from a solvent capable of association, preferably alcoholate, glycolate or alkyl-glycolate;    n = 1-16.    USE -   The method is used in the separation of a hydroxy-carboxylic acids from industrial and agricultural waste liquor or bio-technological fermentation broths. The (di)aminium (di)lactates obtained are intermediates for di-lactides, which can be converted into biodegradable polyesters useful e.g. as carriers in retard drug formulations or as surgical sutures or implants in human and veterinary medicine (see DE 2501448) (all claimed).    ADVANTAGE -   The method provides a simpler and more efficient route to di-lactides than prior art processes known, e.g. from DE 1234703, US 4727163, EP 261572, DE 1720211, DE 4022257 and DE 4318456.    Yields of (V) are typically 74-98%.