How to Clean USB Pendrive with installed ubuntu gnome 16.4 encrypted (with passphrase) that wont mount - Ask Ubuntu

i installed ubuntu gnome 16.10 or 16.4 on usb pqi mini 16gb, encrypted , have passphrase. after few launches crashed, liked ubuntu , installed on ssd. when want clean pqi mini old system cant mount it...

here checks:

sudo dmesg | tail -20 

[116206.287030] usb 2-1.2: usbfs: process 5543 (threadweaver::t) did not claim interface 0 before use [116206.368385] usb 2-1.2: reset high-speed usb device number 4 using ehci-pci [116206.572295] usb 2-1.2: reset high-speed usb device number 4 using ehci-pci [116206.690825] usb 2-1.2: usbfs: process 5543 (threadweaver::t) did not claim interface 0 before use [116206.772265] usb 2-1.2: reset high-speed usb device number 4 using ehci-pci [116206.886786] usb 2-1.2: usbfs: process 5548 (threadweaver::t) did not claim interface 0 before use [116206.886831] usb 2-1.2: usbfs: process 14167 (pool) did not claim interface 0 before use [116206.886851] usb 2-1.2: usbfs: process 5549 (threadweaver::t) did not claim interface 0 before use [116206.886887] usb 2-1.2: usbfs: process 14167 (pool) did not claim interface 0 before use [116206.886891] usb 2-1.2: usbfs: process 5549 (threadweaver::t) did not claim interface 0 before use [116206.886925] usb 2-1.2: usbfs: process 5543 (threadweaver::t) did not claim interface 0 before use [116206.887053] usb 2-1.2: usbfs: process 5549 (threadweaver::t) did not claim interface 0 before use [116206.887058] usb 2-1.2: usbfs: process 14167 (pool) did not claim interface 0 before use [116206.887092] usb 2-1.2: usbfs: process 5543 (threadweaver::t) did not claim interface 0 before use [116206.887174] usb 2-1.2: usbfs: process 5544 (threadweaver::t) did not claim interface 0 before use [116206.887484] usb 2-1.2: usbfs: process 5544 (threadweaver::t) did not claim interface 0 before use [116347.916252] ext4-fs (sdc1): info: recovery required on readonly filesystem [116347.916254] ext4-fs (sdc1): write access unavailable, cannot proceed [116372.971725] signonpluginpro[14581]: segfault @ 7fddeeafbb98 ip 00007fdde89bc5df sp 00007ffcf7c3d490 error 4 in 

libqt5network.so.5.6.1[7fdde8926000+16e000] [116469.963898] signonpluginpro[14919]: segfault @ 7f0ac25e3b98 ip 00007f0abc4a45df sp 00007ffd45bf2e70 error 4 in libqt5network.so.5.6.1[7f0abc40e000+16e000]

sudo fdisk -l

disk /dev/sdc: 14.5 gib, 15504900096 bytes, 30283008 sectors units: sectors of 1 * 512 = 512 bytes sector size (logical/physical): 512 bytes / 512 bytes i/o size (minimum/optimal): 512 bytes / 512 bytes disklabel type: dos disk identifier: 0xa597e4f9

device boot start end sectors size id type /dev/sdc1 *
2048 30281727 30279680 14.4g 83 linux

what should do? tried mount commands found in web. when in gnome-disks click mount, wont mount (with default settings).

have tried dd? mkusb puts layer of safety around dd. can use fill disk 0's, making possible format in windows or linux. may not work if there physical damage.