I had to turn in my old passport when I renewed it .?
They invalidate it and do other back office stuff nothing exciting quite boring really. But everyone has to do this regardless of where in the world you are they almost always send it back to you if its a straightforward renewal only with the top and bottom corners cut and maybe a big red stamp inside saying CANCELLED. The only time its not returned is if its reported lost or stolen but then found or returned to you in which case its entered into the worldwide lost and stolen travel document database operated by interpol its then sent for destruction however your country disposes of passports usually shredded then incinerated.