Jamieson, Fausset and Brown on Zephaniah 1:11

11. Maktesh--rather, "the mortar," a name applied to the valley of Siloam from its hollow shape [Jerome]. The valley between Zion and Mount Olivet, at the eastern extremity of Mount Moriah, where the merchants dwelt. Zec 14:21, "The Canaanite," namely, merchant [Chaldee Version]. The Tyropoeon (that is, cheese-makers') valley below Mount Akra [Rosenmuller]. Better Jerusalem itself, so called as lying in the midst of hills (Is 22:1; Jr 21:13) and as doomed to be the scene of its people being destroyed as corn or drugs are pounded in a mortar (Pr 27:22) [Maurer]. Compare the similar image of a "pot" (Eze 24:3, 6). The reason for the destruction is subjoined, namely, its merchant people's greediness of gain.

all the merchant people--literally, the "Canaanite people": irony: all the merchant people of Jerusalem are very Canaanites in greed for gain and in idolatries (see on Ho 12:7).

all ... that bear silver--loading themselves with that which will prove but a burden (Ha 2:6).